I took all three sciences for A level and don't regret that at all. Physics is an enjoyable a-level, there's a lot less to learn than bio and chem as well (at least on my exam boards) but if you're not confident with manipulating equations it could be intimidating. I found biology the easiest out of the sciences by far as there was more learning facts than applying. I did OCR salters for chemistry which is really fun but the exam papers are so specific you have to know the mark schemes inside out, but if you want to do medicine you'll need chemistry.