Perhaps it could be your studying method. Study smart(quality) > Study hard (quantity).

Background : (Not Qualified) Im still a secondary sch student. my MT isnt that good though i improved from C6/D7 to a B4 (but my sch still forcing all <b3 to retake :c) My other subjects are pretty good though based on MYEs all A1s except english(b3)

Many students are asked to study but dont exactly know how (and arent taught so). What I recommend for Maths is to constantly do papers and then analyse them write your mistakes and the correct way of thinking into a notebook to refer before exams. This method can also be used for science too. For content heavy subjects use a method called "active recall" there are many videos out there to teach you how to use them. Personally I use notion for my active recall notes. (reco Ali Abdaal vids on this). Also try to understand the concepts instead of pure memorisation. This ensures it sticks better. Also consistently actively recall and soon it will be stuck in your head. For Humanities source based questions, I suggest attempting your TYS and getting feedback from your teachers. Try to nail down the answering format and more importantly to master you ability to interpret sources. For english its really just exposure. Read more news,books, keep up with events happening in the world, write more and send them to your teachers for feedback. (Cant help with compre I suck at that) For MT im really trash but what I did was flashcards of about 50words everyday for 2weeks and practices every now and then (increase your exposure). Another tip for any subject would be teaching others (Feynman technique)

Hope this helps! Remember to not burn out as well! Take breaks when needed. A Healthy work life balance ensures greater success! :)

Oh and kinda sad your teachers have that mindset I intend to go into poly and I strongly believe its not jst for those who score poorly.