Breast pain in only one boob?

My right boob has been really really painful these past few days and I don't know why... I don't think it's my period because I'm not due for two weeks (I'm on the pill so I'm like clockwork) and I've never experienced sore boobs at any point in my cycle before. I swapped pills about a month and a half ago to dianette so I wonder if this is the cause because it does like breast pain as a side effect but it seems to suggest both breasts would be sore, not just one. The side effects also list breast cancer so I don't know if I should be worried... I'm only 17 though with no family history of breast cancer so I think it's unlikely. What do you think? Does anyone else get pain in one boob?