Hello medic here, I did maths, chemistry and biology in A levels. Majority of Uni's want chemistry, and some want biology as well. You can do whatever you want as a third subject, you do not have to do maths you can do geography! Also if you want to continue drama for fun, you don't have to study it, most uni's have a vast array of drama societies, which I enjoyed taking part in whilst studying medicine. In fact now working 2 years into the NHS, I am applying to MA acting courses in drama school lol. Also there are many other factors to play when applying to med school such as the personal statement, UCAT/BMAT and interviews. As long as you have both chemistry and biology you should be fine!