i think that you should make your decision purely based off of your desires and not your fears. if becoming a doctor is something you truly want, ignore how difficult or challenging it'll be & just work your butt off to make sure it happens for you. if it's not really something you want then you really need to figure out what your true dream really is because it doesn't sound like you're very passionate about chemistry (of course i could be wrong but if you already froze your semester then maybe chemistry isn't for you).