I'm in Y12 too, and do Physics:
Think ahead, what do you wanna do when you're older? Even if you don't know the specific job, you've got to have SOME idea, or even a general area of a field. If you want do anything Maths related, or Engineering, you'll want Physics, if not, then nope.
I do Further Maths, Maths and Chem along with it, and I find the quite Mechanics and Applied form of Physics means that I can use the skills learnt in Maths/FM, Maths and Physics ties into each other very well, and a lot of the questions may involve some sort of Mathematic manipulation. Hell, stuff that you learn in Physics or Biology will help vaguely for Chemistry.