find a teacher that you like, or an adult you can trust, ask them to help you sort out a revision timetable, like revise for maths for an hour, then have a break then English kind of thing, if you speak to your teachers to say you are struggling then they might be able to give you some resources or whatever to help you understand, tell your mum that you are really struggling as well, she might be able to help sort out getting some text books and stuff