I did Biology Physics Chem and Maths, and yeah at first it's really hard imo, but it gets easier as the year goes on.
You've just got to be really proactive with your learning: ask your teachers for help after lesson if you don't understand something, use khanacademy/examsolutions/chemguide/s-cool/tsr if you have any questions, or if you don't understand your teacher's explanation.
The hard bit is perhaps getting your head around it, really. Looking back, some of the content that I found impossible at first seems so easy. It's just about perseverance!
Oh and also don't feel **** about yourself if you do badly in mock exams first time around: I revised so much and as really confident, but got a D in my mock exam. Instead of crying over how **** I had done, I used my mistakes to do better in the next paper, and so on.
tl;dr it's hard but by no means impossible, you just have to put the work in.