I'm not super knowledgeable about medicine, but I was looking into it a few months ago before changing my mind about my future career. I think that the courses tend to be quite chemistry based, and a lot of universities require chemistry but not biology, suggesting chemistry is more important than biology for medicine. So if you don't like/aren't very good at chemistry, perhaps a 5 or 6 year long course based around it is not the kind of thing you want to be doing. Although I don't want to deprive you of your dream, and I'm sure if you work hard at your chemistry now, in the future you'll be fine.