I would like to do maths, physics and chemistry at a level ...would that be too difficult to juggle x
We can't really tell you because we don't know you or how you work, I think you just need to think about it. If your sixth form is as good as mine was they will advise you on the courses you pick and they will see whether or not they think you will be able to handle it by your GCSE grades.
I would like to do maths, physics and chemistry at a level ...would that be too difficult to juggle
I'd say that those subjects complement each other nicely with some significant overlap (especially if you will be doing mechanics in Maths). But the most important thing is what you want to do afterwards: that should determine which subject you choose.