Note: I am in yr 13, A-levels with predicted grades: further maths, maths, physics, computer science, EPQ, A*s in all
Firstly, chill out 3/4 of work is quite a lot of school work to do every day AFTER SCHOOL, even for me (my school days are about 6.5 hours). Year 12 has just started, do not burn yourself out. I know you are worried about your A-levels, they do matter but they are not as important as you think for getting uni offers. The way I maintained solid grades is not by constantly studying, studying, studying the stuff i did in school. Thats a waste of time. I take very mathematical subjects but computer science is very memory focused like some of your subjects so I will use it as my point of reference. I would recommend NOT to review your notes you took at school on the same day. Wait a few days, let your brain forget the stuff. Then review the content again weeks after you learned it, then do it once again. This is the least time consuming way to memorize things. In each review session do not go at a slow pace as you will just switch off. In each study session try to study mutliple unrelated topics (switching topics every 45 mins to an hour). Start by looking at the topic and trying to write down as much info as possible about the topic on some scrap paper then actively read out loud whilst rewriting the content you have missed (using pictures as much as possible) ideally using inital notes you have taken on a topic or just your text book. you can through away these brain dump papers. This study technique is called
Active Recall. Each study technique has its pros and cons but atleast this forces you to actively think about your content. If you are doing this already, try out different study techniques but make sure you are always trying recall info so you are actively engaging with your work instead of just note taking.
Do not take offense to this but your ability to learn new things may also be poor. This could be a by product of not exposing your self to new ideas regularly. To solve this just cut some of that study time down and read anything but a text book eg. the news or a classic like the great gatsby. Reading comprehension is crucial for aspiring med students as you have to sit pre-admission exams in yr 13 or the summer of yr 12 (which are beyond important). These test require a strong reading comprehsion and are just as if not more important than your grades on your application. Good news, by doing this, your ability to retain info and comprehend text should improve drastically if you religously read so your grades could go up.
Finally, the best way to improve your grades is to study when your not studying. For me and my friends who also have the same grades, we just surrounded ourselves with content that was somewhat related to, but not entirely to, our subjects. Eg. I watched some maths videos when I was just chilling, doing random things like eating.
https://youtu.be/ltLUadnCyi0 <- this is an example. These types of videos extended my syllabus, yet are interesting, relaxing and do not feel like studying. I think the majority of people who do exceptional in A-levels are ones who love/like there subjects at treat it like a hobby, a passion even, rather than a chore or something they study. No notetaking, no stressing, just enjoy the content, have a think and do not worry about retaining all the info .You want to surround yourself with your subject, apply the concepts you learn to your arbitrary daily thoughts. I think this style of learning is one that I see with most high achieving students. They are free thinkers if I were to be dramatic. In general just push yourself beyond the syllabus as work you found hard in class becomes a piece of cake when you start exposing yourself to more complex ideas. This paragraph's subject is hard to sell to others and explain but trust me after a few weeks it just works. Have a go, if it doesn't work then just stop.
Good luck, hope this helps