Hi
Firstly..don't loose hope! I got my AS results back yesterday and was in a state for a good 5 hours before I saw sense. I got BBCC and was devastated. Then I realised, hey, I didn't revise for English and I'm 6 UMS off a B - i'll boost that, drop my other C and boost one of my B's to an A by working my ass off next year to get ABB.
You can do the same! If you keep that B and work hard to boost Biology to a B. And then retake chem next year? Or, you could try and raise the B to an A, the D to a B and the E to a C = BBB.
This all depends where you were within the boundary, of course in how easy this will be to do. Alternatively you could always resit the year? Are you 100% certain that medicine is for you?