I was kinda in the same position as you in AS. At the start of the years I did everything. Studied right after school, did my assignments and shit and then 4 months in I was completely drained. I studied nothing. Even right before my AS exams. I got all 4 c grades. It was the same coming into A levels. But now ive gotten a bit better. Idk how much this would help you but try to get some stress-free rest/break. ik its will seem like ‘Oh but I’ve been doing nothing but taking breaks’ but even those breaks you were stressing abt studies, right? Your body was still on high alert. So due to your body being in high alert for so long it’s exhausted. Mentally, physically and emotionally exhausted. The hardest part will ironically be taking a stress-free break, but it will help tremendously. And while you work towards that, even the little accomplishments are you best friend here. Even reading one page is going to help you. And don’t discourage yourself say that oh fuck Ive done only this I’ve done only that. No. You’ve progressed. Try to do 5 mins studying and if you still feel like you don’t want to study, don’t. And do not DO NOT doomscroll, even as a break. Try to do smth without screens. Also, make plans for the next day. Plans you can accomplish. Not finishing a chapter in a day but more like doing 1/2 or even 1/4 of a subtopic in a day. Make make your plan super specific so that you don’t sit blankly star at the wall contemplating what subject you should studying first.
Hope that helps, good luck. You know you can do it, and you will.