A level mock struggle?

I got off on a rocky start for my maths A level, i had a poor start on Stats and pure, so naturally in the later topics under those i struggled. with mechanics i was focused and the start, so i ended up getting a pretty good B on my regular progress test, which was a huge improvement from a U. with psychology, i get the "theory?" but when it comes to evaluation, and longer answers, i start struggling. now this was just a bit of background to fill in what my issue is. i struggle with trying, i will sit down for an hour or so, attempting to learn or revise, and then hit a wall, and completely drop it and give up. the same thing happened in GCSEs, but i managed to pull through within the last few weeks. but its not the same for a levels, my last minute bs isnt gonna work. my parents have high expectations of me, and so do my friends. i know i can do it, because ive done things i didnt think i could before, im really good at physical stuff, i learned how to change a basic tire within a couple of minutes a while ago. but when it comes to pen and paper i really struggle, a friend of mine brought up ADHD as a thought, and idk im scared about it, what if i do have ADHD, i also have some symptoms of other stuff, but then on the other hand i always tell myself that its bull and im over-thinking/over-exaggerating and im just using it as an excuse.

ive been told previously "working hard, using past papers, using different sites or resources"
but it doesnt work, not for me, it will help for a short period of time, then ill hit that wall i mentioned again.
sorry for making this really long, i just dont know tbh

TLDR; im struggling at college, scared about mental health, lost in general.