help!!

mily

yesterday i noticed a change in my left breast. it’s a lot bigger than my right, part of it feels firmer and it’s painful to lift my arm and from my underboob to armpit. i’m trying not to freak out but how long should i wait before getting it checked? i’m 16 but i know my boobs pretty well and i know what’s normal for them at different sizes cause i went from a C cup to an A cup from weight loss.