What physics course are you currently enrolled in, at your school?
I'm interested in those big theories too. We're actually doing Quantum Mechanics in my AP Physics C class right now (yes, in my senior year of high school).
Okay, to start off, to understand concepts like quantum mechanics, you need a very solid understanding of functions and calculus. Actually, pretty much all advanced physics requires a good background in calculus. You can obviously read through the theories and get a good grasp of it without going too deep into the mathematical derivation of how they come about, that should work well.
Relativity (especially special relativity and simultaneity) is tons of fun, when you deal with all kinds of paradoxes and all.
The basis of all physics is a strong mathematical background. Trust me, it'll help you in the long run. Physics and math go hand-in-hand. If you don't understand functions visually, you'll never understand physical (mostly abstract) wave functions when you learn quantum mechanics.
Particle physics is very very essential too (behavior of protons/electrons/neutrons and other forms of particles).
I can see why you're interested in such theories, lot of people are. Just do some self-research / studying on your own, it'll help you out later. All in all, good luck!