Sore breasts

So, I have had sore breasts/nipples for about 2 weeks now. I mean, nearly tender to the touch!! I've been on bc for nearly 3 years now and since starting it I've never had sore breasts/nipples. My period is about a week away, but again, this hasn't happened for years.. Could it be a sign of pregnancy possibly? I've heard of people taking their bc correctly and still becoming pregnant. Is that it? Or is there some other explanation?