Probably wrong attitude. Instead of thinking only your opponents threats try to generate some play on your own. For example, in this game you could try 15... f5 to be followed with e5/g5 to start your own attack on the kingside. If you only defend then it will be difficult.
By the way, next time you post state clearly which colors you were using so that we don't have to spend time guessing.
Here is a thought. Not meant to offend you. The following question is an honest inquiry about your chess knowledge.
Do you know when the opening ends and the middlegame begins?
If you do please explain it in specific detail. Pretend that I am a beginner in chess and you are explaining it to me so that even I can understand.
I would say that these modern openings are pretty prone to you having to defend during the middlegame (i'm not bashing these openings, I love to play them). You allow your opponent to build up a center and a space advantage, the point is that at one point you should manage to prove that you can generate play thanks to his position that isn't strenghened enough (more difficult to protect a large than a small territory). However keep in mind that when you allow him to get this space advantage, you offer him more room to manoeuver, his pieces can go faster from one side of the board to the other, and so it's generally easier for him to build an initiative (or "attack").
That being said, I'm not bashing the opening choice at all!
Just gonna give a few ideas more than moves to help you think about and generate play instead of having to respond to your ennemies attacks:
At move 5.Nc3, white is trying to have a firm grip on the d5 square. Almost all his opening moves are aimed at the control of this square. This means that if you can manage to get the control back on this square (your e6 pawn already prevents his pieces from getting there, and could eventually support a pawn there fighting for space) without getting into troubles in exchange, then you would have disupted his opening moves while yours would have been useful, this would generate some dynamic things around that area that should favor you. With this idea, we might think about sustaining a d5 push.
another idea might be to see that his d4 square is a nice post for one of your knights as he couldn't get chased away by a pawn anymore, thus trying to fix this weakness to make use of the square might also be a good plan (thus c5, Nc6 and g6/Bg7 plan might help get some activity). One problem of this plan is that by playing g6, you are weakening your dark squares (not that it makes the plan bad, just be aware of it, it's often good as black to make some concessions in exchange for some activity). another problem is that after haviing played e6, you could have developped your Bishop already, thus you are making a second pawn move to develop the bishop. This is a tempo down. With the plan of controling the d4 square I wouldn't have played e6 but went for g6 directly. for example with the Nf6-d6-Nd7-Bg7 sequence.
Once e6 was played, I would have gone with the d7-d5 plan.
These are just ideas, not saying what should have been played, just what could have been more coherent.
10...Nxe2 seems strange. You spent a lot of time securing a nice square and bringing your knight here and you exchange it for a bishop who can barely see anything else than his pawns. You could have kept your knight in here and letting his bishop stay in the way of his pieces, thus limiting the possibilities of manoeuvering. You can still exchange this if you plan on opening the center, but as long as it is closed knights are "generally" stronger than bishops. Unless it was part of a plan I didn't see of course (I'm still quite a bad player after all).
After h6, you allow him to play Be3, and you can notice that now he has the full control of the d4 square. This means that all the moves you played in your opening which were aimed at this square have been done in vain. This is the exact situation I explained earlier in this post: you are now in trouble because the area where you aimed your moves is no longer under your control. If white manages to play d4 anytime soon you will be under a storm I suppose. In the actual game white didn't play d3-d4, and I really think this is a mistake by him.
13...0-0-0
Wow! This move is your doom I think. You decide to castle long (likely because catling short would give out your h6 pawn, which further highlights the problems of your h7-h6 move earlier), in a position where you lost the control of the center. If white play d3-d4 now I think ost tactics that may appear will favor your oppnnent. If you had in mind to go opposite castling to attack your opponent, tmember that an attack on a side is most of the time countered by active play in the center. Given the obvious move for white it d3-d4, opening out the center, and giving all his pieces scope to get active, a kingside attack is likely to be a bad idea. And even if white doesn't play d3-d4, your long castle already has a lot of holes, so an attack by white on your king should allways be faster that your attack on his king (he has more development, more control on the center, and your king's position isn't safe at all. To me it's this move which sends you in big troubles for after the game.
for what happened after, white gave pieces away, failed to play d3-d4, gave you back the control of d4 and gets mated on a tactic.
With absolutely no calculations involved, I would advise to play 0-0 instead of h6 on move 11. The very next move I wouldn't have gone Qc7. Okay you lost d4 but this was at the price for white to remove one of the controlers of d5, so my plan would have been to try and achieve a d7-d5 break. Not now because the king is still in the center sure, and the h6 pawn is still hanging. However for the reasons given earlier i wouldn't send the king on the queenside. 12....f7-f5 seems logical to me, it attacks one of white's supporters of d5, clears the f7 square for the king to walk to f7 if we need the h8 rook in the game fast. also note that if white takes on f5 and you recapture with the knight, you get back some control over d4, clear one of white's controllers of d5, get some space in the center. I would try to sold the problem of king safety by making him walk all the way to h7 (since the plan is to play with the d5 square, it would open the center (which akes sense now you have a bishop paie and he doesn't) and it's likely not a good idea to open the center with our king still here.
Now after you played 12----Qc7, and instead of 0-0-0 it's much tougher. f7-f5 lost a lot of interest because retaking with the knight would allow white to open the pawns around our king by trading them, 13....d7-d5 seem extremely dangerous because of 14....d4 which would blast open the center with our king still in the middle. Also we removed our queen to support d5 so not really the plan anymore. Maybe getting back to the control of d5 by playing 13....Nc6, strenghening both the d4 and b4 square and which could maybe prevent white from playing d3-d4 with a strong initiative (needs to be calculated). If white can't open the center then we have the time to either castle long and go with f5 with the idea of opening lines, or make our king walk all the way to h7.
Note that I never considered h6-h5 to be able to castle short, because it would open even more holes around the area where we would want to pur our king, not a good idea at all unless you know you calculate like a god and can defend it (not my case), or in the position your opponent has no way to take advantage of these holes in the immediate future (not the case at all!).
In short: try to aim your moves at doing something right from the opening. It's especially more important with these modern openings where there is less chance to lose because of fast mating patterns, so you have more space to develop all your pieces around a common plan, which will ensure that you will have active possibilities in the midgame.
Also please note that I involved only 1 calculation in this post, and that calculation was only one half-move deep (white can respond with d3-d4 to our d7-d5 push and blask open the center). This means that you don't need to be garry kasparov to take a grasp at what is going on on the board.
Hoping this post will help you.
Thanks
Wow. DoctorFuu’s post was one of the most comprehensive, informative posts I have seen by anyone ever. 
Maybe out of topic. Reduce coffee consumption. Too much caffeine in the body makes us easily nervous.
For me, chess is a state of mind. I used to get tensed up during the midgame. Then I realized that patience is required. Patience leads to calm. A calm mind is a clear mind.
What are your goals for playing chess? If all you think about is your rating, you will be unhappy.
All players improve over time if they make an effort - even a small effort.
Actually the position still seems interesting after 28..e5 Here are some sample lines.
Whether I win or lose, I'm always on the "receiving end" during the mid-game. Here's an example of the last game I just played. Even though I won, it's nerve wracking. The pressure is starting to make me not want to play anymore. I always feel like David vs Goliath.
I honestly have the same feeling as you, but then I realize when I play nervously, I end up making blunders. I usually feel nervous when I'm playing with tough players. It's normal to feel nervous during a mid-game as that's when most blunders happen.
Whether I win or lose, I'm always on the "receiving end" during the mid-game. Here's an example of the last game I just played. Even though I won, it's nerve wracking. The pressure is starting to make me not want to play anymore. I always feel like David vs Goliath.