I'm on to my second year of a levels in biology, chemistry and physics. Physics is definitely the hardest one for me, but it does make the others seem easier in comparison and helps change the way you think so you can answer questions for biolgoy and chemistry easier. It's hard work but if you are committed you can definitely do it! Biology is mostly memorisation. Physics is more application of math skills so as long as you do lots of pratice you'll be fine. Chemistry is somewhere in the middle but if you can handle math in physics, you'll be fine with the math in chemistry. Good luck!