Help!

So, i am 16 years old i feel a flat lump on the top of my left breast. It is painful to the touch and bumpy. I can feel it if i move my shoulders a certain way or take deep breaths. I dont know if i should be worried. I do not remember hitting it on anything or having any trama to the area at all. Should I wait a couple of days and see how it is or have it checked asap?