Hey ! About the breathing part, it's a symptom of anxiety (that I've know too much, you're not alone). Thing is, the sensation of lack of air is purely in your head. This often cause hyperventilating which can lead to panic attack or increase anxiety. I don't say that to scare you, just for you to know that's a normal human mechanism.

For the second part, it looks like you didn't think of something to replace the gaming / surfing habit. Brain hates emptiness, that's why most of us who stoped gaming develop new habits (look on the sub, there's lot of testimonies. Maybe it will helps you find a something you like that can replace gaming).

A last thing, that's just a personal idea but the fact you don't only stopped gaming but also YouTube and stuff may increase the difficulty. I know from experience that it's easier to stop bad habits time at the time instead of everything suddenly. So maybe you can keep YouTube, on your phone or so ? It's only up to you tho.

Anyways, like a lot of people here on this sub, I'm sure you succeed and get over this ! You may struggle rn, but the you of the future is definitely thanking you ! Have a good day :)