I am in yr 13 and the last October I changed subjects. I originally did Politics, history, and philosophy. On October 15th, 2021, I changed to a bio, and chem and kept philosophy. I am happy with my decision but from my experience, you learn A LOT in the first half term, you learn the foundations of the subjects and personally, for me, it was hard to catch up on the missed work without going over it in class. But I managed to go over it.
I know that I switched to stem subjects and you're switching to nonstem subjects but I presume it will be a similar experience to mine when you switch. If you want to do medicine ], you have to be set on it, your heart and mind must say that medicine is the right career for you if you don't have that passion to pursue the career, then you won't be accepted.
Basically, what I am saying is be 100% sure that you want to switch as it may be that you don't like a certain topic in your subjects or it may get better soon, look at the career prospects that the subjects you are changing to will be and ask people for their experience in the subjects. But if that is what you really want to do, then go for it, because there is no point in doing subjects which you hate and getting a bad grade in the end. You need to enjoy the subject to succeed. Good Luck!