What Causes Soreness In Breast After Taking Plan B?

I will like to know the possibility of pregnancy in the following scenario: My boyfriend and I had sex during the first day of my period. We did used a condom but it broke, he felt it and pulled out before he ejaculated but the next day i took a plan b pill. A few days later the same thing happened but since it was the first sunday of my period I began taking birth control. I'm little freaked out about being pregnant as my breast are a bit sore. This all happened last week