How do I limit counter-play?

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!