Anyone have any study tips to help with college?

I'm in my first year of college (UK so 16-18) and I'm drowning in the workload. My college sets us on average 4.5 hours of homework per subject a week. This is taking its toll on me as I find it EXTREMELY hard to do any homework before the day before it's due. I've tried looking for study tips but most suggest frequent breaks, which doesn't really work for me because one 15 minute break turns into 3 hours of nothing. I also dislike short breaks because it means all I'm thinking about it how close more schoolwork is. I am genuinely trying to improve my habits but it's just so difficult when I never learn my lesson, and it's really affecting my mental health. Ive only really come to terms with the fact my lack of revision isn't just I never learned how to revise this year, and getting a diagnosis before my a levels is just not possible with the wait times of the NHS