Male: my right nipple has a hard lump behind it? HELP PLEASE!?

Hi my name is James. i am a 13 1/2 year old male. and i have this lump behind my right nipple, it hurts to press on it and i can see the veins going through it if i look in the mirror. it is a little bigger than my other one, and it always looks round (unlike my other one) and when i sit down it "sags" lower than the left. Also, it happened before and then went away when i noticed it i felt the lump, and it was the same size as the other lump behind my left 1. but the my brother gave me a "titty-twister....>:(" and it came back...now it's staying...... Please Help!