Sore breasts...why?

Emily
My breasts and nipples have been extremely sore lately(2 weeks). Not just sore, aching. It hurts to put a bra on and take it off, and at work I have to wear a sports bra over my bra to reduce movement to help with the pain.
What could cause this?? 
P.S. I am due to start on 11/16, I do normally have tenderness before my periods but by the time I actually start it will be going on 3 weeks of constant pain.