How can I relax despite my nerves?

[Okay]

I'm a nervous person and I can't really relax or focus any more. I have some exams coming up and I'm struggling to revise for them because every time I try to, I get really down that I can't do something or really annoyed that I got something wrong. And when I try to relax, I don't know how. I try to play games (on the computer or on my Xbox) but I either lose focus or get annoyed that I'm not good at the game. I end up just surfing the internet, observing rather than contributing. I think this is all due to my nerves, but probably not entirely due to JUST that. I generally get nervous if I do write something and then post it, like on twitter or on here.

I feel like people won't like me or what I've wrote. I also tend to go to bed really late because I feel if I stay up late, I might be able to relax, kind of like I'm escaping from the day life (I never can relax though). This question is sort of a catharsis for me, getting all of this out, but I'd also appreciate any suggestions on what to do about any of this. I don't want to go to the doctors, so please don't suggest that.

This might not be a serious enough problem for the Mental Health category, and I'm sorry if it isn't.

Thank you for reading this/that.
IDK which answer to pick as best. Sorry.