First off, I'm sorry to hear that you're going through all this! It sounds like a really tough time. Just wanted to reiterate Caitlynk_22's words and also say that everyone here on AN is here to support you (I know we're internet strangers, but AN is highkey one of the most supportive communities going around). I hope you don't feel alone in your suffering and find some comfort in that a lot of other people have been in your shoes.
I can't really give any subject specific advice because I'm an oldie that finished HS several years ago, but I think a few really good things to do would be:
1) Speak to your teachers about how you're struggling at the moment. They'll have gone through this with many students previously and hopefully be able to give you some good tips
2) Chat to your school counsellor if you have one! You don't have to have diagnosed mental health issues to speak to a counsellor. They'll have heaps of expertise in exactly the sort of stuff you're going through and I think it's really helpful to have someone you can vent to and who can offer some good, impartial advice.
3) Find times for the things you enjoy - life isn't just about school, no matter what anyone else says. Are there any sports or activities you're interested in?
4) Exercise - ties into point 3 but if you're not into any sports, just try to go for regular walks. It's great for clearing your head, you get some alone time, and you get the exercise endorphins
Ultimately, all you can do is try your best. It can be incredibly hard, but try to not compare yourself to others. Your journey is yours alone and as long as you make an effort that you're proud of, nothing else matters.