I am so anxious!

I’ve got anxiety problems, and when it comes to exams, I always have a mental breakdown... I don’t know, I do study but my brain never works! I don’t know how to do well at my GCSE exams. I want at least 5A*s to be happy but I feel like I have no time to do a good revision. I have started already and finished half of 3 subjects but I feel I have started forgetting. I NEED to do well. Any tips to help my brain work properly rather than sleeping and eating well? Also any motivation tips? Improving memory? Doing well? Omg I am so destroyed. 😣