How do I stop making mistakes

Stop playing speed chess. And before you say dont play speed chess. Look at your last G15/10:

https://www.chess.com/game/live/144733012496?username=xkaythemanx&move=0

You lost in 38 and moves and still had 13:59 on your clock.

So if I should stop playing speed chess, how fast should I play?

You should play whatever time control you want to play. But when it comes to improvement?

At least G45 if you're serious about actually improving. To give you an idea of what Im talking about. On each move you need to ask yourself the following questions:

Am I following opening principles?

Are my pieces safe?

What is my opponent trying to do? What is my opponents plans?

What is my plan? What am i trying to accomplish?

If youre not giving yourself enough on each move to ask these questions then youre playing too fast. But like I said. Play whatever time control makes the game fun. But growth and playing fast dont work.

Hello there. What I can really see watching your game is your thought process needs to be trained for real above all. Just only improving in this aspect, your game is going to level up and you are going to start to play without those huge mistakes as well as you will progress in other main aspects of chess. 
Grettings,

IM Arnaldo Fernandez de la Vara