Shooting pain in right boob??

Anna
Hey everyone! I'm 21 and I, like most other females, get achy boobs during PMS, but for the first time ever I'm getting a really sharp pain going from the right, mid-boob, to under my nipple. It hurts so bad! Any idea what this might be? It just started today. Thanks!!
Also, yes I am sexually active.
I am not on any form of birth control.