I started my A Levels doing maths, English lit, biology and chemistry. I got a B at GCSE but I probably could have done better so decided to try it anyway and I feel compared to other core subjects it's disproportionately hard. I ended up quitting at Christmas and swapping maths for history and re starting in September. I'd say unless you feel like you have a flair for it then avoid- I knew a lot of people who went from an A at GCSE to an E/U at A Level. Good luck you!