Sore breasts

My breasts are always sore!  Does anyone know what might cause this or what I can do?  In the beginning I thought it was from breast feeding but I've been done with that for over a year now.  Started birth control about five months ago that hasn't changed anything.  It's only a real issue when I'm playing with my toddler.  It hurts so bad if he accidentally knocks into my chest. Any help would be appreciated!