I was hoping that someone could help me with a major problem that I have had lately playing chess. Over the past few months I have lost over 200 points on my online rating despite having played frequently.

The real problem that I am getting to though is that I have consistently had an overwhelming positional advantage, but I have somehow managed to lose it and the game very frequently. Here are a few examples.

I feel like surely there must have been a way to finish that game without letting my opponent get all those passed pawns. Here is another game where I lost largely due to time pressure but also due to letting my opponent have an active queen.

I understand that there are certain moves I could have made differently, such as winning the exchange in the latter game. What I would really like for advice though is that pertaining to limiting my opponent's counterplay as I presume that that is a serious weakness that is a main cause of the problem and perhaps even the root of the time pressure I experienced in both games. If you think there is something else that might help me please share though. Any  help would be appreciated!

Game 1.  I don't know the opening, but after he got his active queen, you defended well and got to an  endgame fine.  After move 24, you were confident that you would win but I think it's complicated and I believe you are better but not much.

29...Rxf2+ probably still works but I would try to get rid of those pawns on the queenside asap.  Your win comes from your two passers and any counterplay occurs because of his passed queenside pawn, so I would play axb4 first for sure.

Maybe 30....Ra2 is better.

After 34.a6, I doubt you can win this.  Your rook is horribly placed.  In a way you got a bit unlucky in that you could never get your rook on an open file to give checks from the side or get your rook behind his passer.  This may be one of those positions where it looks like you can play just about anything, but it turns out differently.  More precise play was required.  And yes you could draw this but you chose to try and win which is fine. 

2nd game.  You obviously had a completely winning game.  You dont seem to know how to finish this.  It happens.  

Looks like you missed another win after 35.Nxe6.

40.Rb7 is probably fine, but I prefer a move like Qe4 (stops any Qe1 stuff, eyes the rook on c6, eyes a8 etc).  Any time I can centralize my queen like that I'm going to do it.  The win is just a matter of creating a few weaknesses and not doing anything stupid.  h4 and h5 later if he lets you.  Then some kingside pawn pushes to open him up, a rook lift maybe. 

After that, you got into time pressure and lost, it happens.