QUOTE(Kcdw96 @ May 13 2017, 03:23 PM)
If I were you, I'd start on a course on discrete mathematics. It helps you to view maths from a different perspective, ie the logic and intuition behind relatively simple facts like why 1+1=2 or why is e irrational?
After that, I would follow up on a course on linear algebra and probability, things which for some reason, are not taught much in school.
In my opinion, studying more calculus is not as useful as studying the above topics, as A level maths (if you get a good grade) already provides a good foundation for studying and understanding calculus concepts, should the need arise. Meaning, should you see a differential equation you don't understand, chances are that after googling for a while you should be able to understand it on your own.
Firstly, TS is interested in physics. Discrete mathematics, while fun, has no immediate relevance. Calculus, however, is absolutely crucial. When I say calculus, I mean all the necessary methods a physicist needs: differential & integral calculus of one and several variables, complex methods, differential equations, fourier analysis, and so on, which are not covered in A-Level Mathematics.
I find your comment that A-Level Mathematics provides a good foundation for understanding calculus puzzling. I'd say A-Level Mathematics is close to useless when it comes to university level mathematics or mathematical methods for the sciences. It's just a hoop everyone is expected to jump over.