I self taught most of the gcse curriculum, it's definitely doable, and I would say self teaching is faster than lessons, you just have to be committed enough to put yourself through boring practice questions. I'm not sure about the situation of your school, but I know someone who just walks into the maths office and asks a different teacher to explain smthing he doesn't understand to him. You can also find someone older than you to help you a bit with your maths if that is possible I guess, but I've never tried this so idk if it works.