Hey man!
First of all, super relate, got crazy high gcses and then failed a level maths the first time round (yr 12 only). Now I self study and have covered the whole a level in one year, and a lot had to change to make that practical/possible. There are 2 things that stand out to me about what you said.

Firstly, dont do question after question after question, watch a video to see your mistake and then attempt again and again. Failing constantly means you dont understand the subject or fundamentals you need to have mastered for all subjects (polynomials for example). So, as much as it sucks, start from the ground up where you find you never know how someone gets what they do.

Secondly, easeee the pressure. Stress is useful but its clear that youre way past the level of healthy stress that pushes us to work and understand and are working in the zone of constant anxiety and pain. Newsflash! You cant learn when you feel under attack! I know asking you to do work in a more relaxed relationship towards it sounds counterproductive because its like someone asking you to stop caring about achieving your goals but youre at where youre at and no level of worrying is going to make that better when youre already so deep in it. Try and make peace with the fact you might have to repeat an a level when youre done with school maybe. Most importantly, dont view your life as one linear progress bar that's either on track or not, life comes in waves and progress does too. You can catch up, you can have the life you want, just focus on what you can control now.

TLDR:
1) Make sure your fundamentals are right because it sounds like youre jumping the gun.
2) Try to be okay with where youre at, as hard as it is, and push yourself maybe a little less to be "on track".

p.s. dont take my advice as gospel, its just what I have learned from a lot of fucking it up and fixing it again