Applying for medicine at UK a university..?

Hey, over the last couple of days i've been seriously thinking about which direction i want to take my life in, i never really had a clear idea of what i wanted to do do at/after university, and i figured i needed to make a descision at some point, and i really want to have a bash at medicine but i'm not sure if i'm too late. I'm currently studying Maths, Chemistry, Physics and Theatre Studies at AS level and i'm predicted A's in all of them. i got 9 A*s and 2 A's at GCSE, but a lot of people are saying you need biology at A level if you stand any chance of getting into medicine at university, especially at Durham which is where i'm thinking of applying. I need information/guidance fast because i've left it very late and have almost no work experience or anything medical related to go on my UCAS, and i'm not sure what to do.. Not just that aren't there exams you have to take? I really need some help, do i stand a chance?