Sore/sensitive breasts/nipples.

So this is an odd subject for me, but last week and this week my breasts have been very sore. And my nipples have been super sensitive and around them has been sore. I've been on birth control for nearly 3 years now, and they have never been sore since starting it. My period is also a week away. But like I said, since I started birth control I've never had sore or tender breasts/nipples. Any idea what is going on? I'm just confused..