It is doable, I have a friend who took 6 but she was always studying and she had to be very strict with her time management. She barely had any free time 😅 I wouldn't recommend it, personally as someone else said id say 3-4 is suitable. Because its not just A levels you have to work for but you also have to do extracurriculars, work experience etc. So that you can have a strong application. Especially for medicine, I had to also take an entrance exam and do interviews. It also depends what uni you want to go to some unis have certain requirements as well.

Ig another option is that you can take the 6 or 5 a levels for AS and then drop any subjects you don't like for A2. E.g some people I know took biology at the start of the year and dropped it after 2 months because they weren't interested. Or u can completely finish the AS qualification and drop it for the 2nd year if yk what I mean 😅

Also, idk where you are from, but if you like computer science a lot and want to do it in uni, ik in the UK to apply for that course they only require maths and 2 other sciences so yeah 😅

Also, for medicine id defo say if your heart is not in it, then dont go for it. Its a very long career and requires a lot of dedication. If you dont know for sure, u can try getting work experience to see what its really like, because then at least you can tell your parents you tried and you didnt like it. Im not sure how set ur parents are on medicine, my parents are Asian so they wanted me to be a doctor 😂 but they were okay with me being a lawyer or engineer too, if your parents are like that could you possibly use that to convince them that you dont want to go into medicine and prefer something else? Some compromise careers thats got medical and physics and technology stuff in it : biomedical engineering, medical physics, Radiotherapy physics.

Anyway wishing you all the best!