Breasts hurt when growing?

Okay, let me start with...I am 21. So I guess I am probably still growing. I noticed for this past week I've been having small bouts of pain that lasts about 15-30 seconds right where my breasts begin. Now when I actually squeeze my breast or feel it, it doesn't hurt me at all. Yet there is this sorta pain there. I remember reading a while back that when your breasts are growing it hurts a little and I do know I'm not pregnant so that's out of the picture and I'm currently not taking any birth control or prescription drugs. I don't remember having any pain when I was growing up and my breasts just started to grow but they definitely aren't fully developed yet and have a ways to go...so do you think at 21 my breasts are growing and giving me a few aches and pains now and then? and why only now?