4A/A* students how do you not struggle doing independent study.

I'm in yr12 and I've done barely any independent study and at this rate I'm going to fail my a levels. I'm doing maths, fm, physics and cs and playing 2 instrumens as well. I only have 4 free periods a week so I have to do work at home really. In school hours I don't really want to do any independent work except cs sometimes as I'm just mentally tired of maths by the time I have a free. Its also the same after school after spending almost the whole school day doing maths the last thing I want to do is maths or work in general. I'm tired physically and mentally by that point. How do you cope with the workload? When I try and do independent study I just constantly get distracted do something else like looking at some off topic thing related to the subject I'm aiming at doing and I constantly procrastinate. In general I find it really hard to focus since I get distracted at home all the time. How do you not procrastinate at home and focus?