Did you struggle with maths at GCSE? Cos if you struggled to get that A, then the A-Level perhaps isn't for you. However, if you got the A without much effort, then it'd be a good choice. To be honest, probably a better choice than history, as it's useful to have 3 sciences for medicine...apparently as it's so competitive, the BMAT is used to seperate the best applicants, for which maths/physics is really useful, but by no means necessary.