Well maybe you could try sticking with Politics for a few weeks to get used to the course and then decided if its definitely not for you or not. My school allowed us to change out options if we wanted once we had started lessons and realised we didn't like it etc. Does your school do that?
Sociology is political, but obviously not as much so as politics itself. It looks good on the old UCAS form, and if you got an A* at gcse for sociology you should be fine.
I agree that you have to love your subjects, but if you've got 3 that you love already, it should make it easier to take one you don't love so much.