helping bf with his mental health?

so i’m 17, he’s 18 and we’re both quickly approaching our a-level exams. he’s never been one to get stressed over schoolwork mainly bc he doesn’t put a lot of effort in yet still gets by on his intelligence.

recently, his teacher has taken away the majority of his free periods for him to attend extra lessons/go sit in her room and do work, and he’s just in a constant bad mood because of it. he’s not a fan of academia and he just feels like the weeks are so repetitive (constant school work, then he’s been going to actual work from like 6-10:30 each night recently) and it’s going to be like this until june when our exams end.

i can’t help the fact that he’s having to do schoolwork/go to work, but i’m just not sure how to support him bc he’s been feeling so down recently and i hate it bc he’s not himself, he’s been a bit snappy (not really at me but i feel like every time i try and be positive about something he thinks of some criticism). of course i always tell him i’m there for him and i’m here if he needs to vent, and i ask him how his day’s been/how he’s feeling and try my best to help him but i’m just not sure how to make him feel any better and honestly that’s all i want. don’t get me wrong, when i’m with him outside of school he’s generally fine and he can be fine in school too but he’s just generally unhappy. we’ve been together 6 months now & this is my first real relationship so i just don’t know how i can best be there for him other than what i’m already doing, so any advice would be great, thanks :) (sorry this was so long)