Beside all the ggood advice given above, talk to your teacher(s). If you're having trouble in a subject, they can give advice, tips on how to look at the subject, point you toward a tutor, any number of things. I've known many a college professor here in the USA to say of a student,"If only they'd asked..."
Talking to your parents about choosing your scholastic battles wisely is a Very Good Idea. I tried to tough it out, and ended up with mononucleosis from the stress.