why is it that my breasts will only hurt when i'm NOT on my period? i've been taking birth control for 4 months now and every since i started the 2nd pack of birth control, my breasts grew a whole cup and they started to hurt. whenever i got my period, the pain would go away. but as soon as i stopped bleeding, my breasts started to hurt again. they feel like their bruised, just a real achy feeling. can anyone tell me why this is? could it be the birth control that causes my breasts to hurt?