This is purely my own personal view:
But I would do Chemistry (we've established it's almost a must) instead of Psychology.
I did Psychology for AS because I thought it would interest me, and I still have respect/interest for the subject in general. But at AS/A-level? It was disappointing. There was no real discussion or exploration of Psychology at all. From what I recall it was like a weird mix of a bit of statistics, a bit of making ad verbatim arguments for and against various study designs, and memorising endless key studies. It was like the study of the study of Psychology, not the subject itself. I felt it really let the subject material down. We also spent at least a few lessons doing things like making hats, colouring, watching films.. I'm not a complete square, but an entire lesson making hats?
I dropped it even though it was my best mark, I found it that uninspiring.
EDIT: I think it would be daft to go on my hearsay alone, though. You might feel very differently or the course might be different now or where you are. A lot can depend on the teacher. Why don't you start with Bio, Chem, Physics, Psych and History and decide which one to drop after a period of weeks? This can't do you any harm. You can even do 5 AS levels, it's perfectly possible - but ofc don't compromise your grades to do this if you are struggling with a key subject for medicine.