How to get rid of brain fog?

Depression has generally made my mind into mush, but this is too far. I struggle to focus and cannot memorise anything for longer than an hour, and it’s exceedingly difficult to pierce concepts together. I’ve tried everything: sleeping beforehand, getting enough sleep at night, eating healthy,limiting screen time- nothing works. I literally can’t remember anything, can’t focus and start getting headaches the longer I stare at the papers. My brain feels foggy, deepfried, like there’s cotton swirling around in my cranium instead.

Can someone please help? Idk what else to do, I have some important exams in April and NEED good grades.