Hi i get exactly how you feel, I was the same when it came to sitting mine last year; especially if you have stuff going on outside of school aswell. I know it's easier said then done but you need to push though the last few weeks of exams and do as much revision and preparation that you can for all your subject, because then you'll have the whole summer to relax and when you get your results you can pleased that you know you've tried your best no matter what the grades are. Some tips for you are:
1) Also make sure that you have a designated time just for yourself that you never do any work it can be whenever you want, but try to always stick to it, otherwise you will wear your self out
2) Whenever you go into an exam make sure you read/answer all your questions carefully and if can't answer a questtion move on and come back don't sit there and stare at it (I found i did that alot in my mocks and ended up running out of time)
3) Finally, answer all of your question even if you think you wrote absolute nonsense, beauces you never know if you could get a mark and that could be the difference between a grade
Also please remember that as long as you try your best that's all that matters, I know sometime that friends and family may create extra pressure on what grade you should get but it ultimately doesn't matter and much as you think and isn't worth that much stress. If you do get all 9's that's amazing, but even if you don't it's not the end of the world.
Sorry that this is so long, but I hope it helps, feel free to message me if you want any help with anything 🙂