Fine until midgame, then collapse

Hi,  I started playing again after maybe 10 years. I was never good, used to be ranked about 1200 at best, so I was quite happy that I was holding my own in the 1050,1100 range for the first week or so.

Then I started playing in less ideal situations (subways, other tabs open, distractions etc) and slid below 1000. Since then, no matter where I play I can't seem to win a game! I do well enough in the opening and first half of midgame (nothing to write books about, but better than my opponent), and then I get pummeled.

Here's a recent example. I was being overly aggressive with my queen, which I know is bad form, but I noticed it was effective at this skill level in past games. I get a free Bishop by move 5,  exchange queens, and by move 20 I have 2 rooks, 2 bishops, and 1 knight, and he has 1 rook, 1 bishop and 1 knight. Then I mishandle his advance pawn and all hell breaks loose, and by move 45 I have to resign.

https://www.chess.com/live/game/2250953247

What am I doing wrong?

20...Bxd3+ was a better try. Both your knight and your bishop are under attack. If the knight moves, the bishop will be defenceless. Playing Bxd3+ first ensures that the soon-to-be-hanging bishop trades itself with another bishop first with a check, and by the rules of chess White will be compelled to stop the check, and thereafter Black can move the knight to safety. The passed c7 pawn is not sufficiently strong enough for promotion threats, so the game is more or less won by Black.

Move 28 you hung your bishop. Move 31 you hung your rook. Your opponent didn't trap these pieces or trick you with a double attack or crafty fork - you placed them where they could be captured. Even with all the dubious early play you were winning easily. If you can play full games without losing a piece for nothing you will gain several hundred rating points. Until you stop doing that you will get nowhere. I guess just try to concentrate on what is going on.

Playing slower helps and only in situations where you can focus.  If you play on the subway, you are almost by definition saying "I don't give a &^! if I win or not" and that kind of attitude is toxic poison that encourages bad habits.  If you need someone to talk to you about a proper thought process to use every move, a lot has been written on that, but it is all basic stuff that you should be able to figure out on your own like look at all checks & captures both sides can do every move.  Don't just focus on your plan, ask what your opponent is trying to do and will do in response to your planned move.  

Thanks for all the tips!

Has anybody done a eye tracking study of where grandmasters look while analyzing a board?

Read weapons of chess by Bruce pandolfini. This will help on your elementary basics of the game.