What Do Sore Breasts And Nipples With Lower Back Pain While On Birth Control Suggest?

I was on the depo birth control shot or maybe a year or less. The last time I got the shot was the end of September. I am experiencing breast and nipple soreness and tenderness and lower back pain and have been for about four days. My breasts also seem a little swollen. I took a pregnancy test four days ago and it read negative. Just wondering what you make of this?