Ok I'm 15 and I am getting worried. 3 days ago my nipple started hurting. And yesterday I felt like a lump directly under my nipple about the size of the end of a pen you don't i repeat don't write with. And everytime I press it it hurts. It's not visible. It's under my skin. And it's about a week before I start my period. I am on birth control but not sexually active. I just want to know what it is. Don't just say go to the doctor...help me out.