What Causes Tiny Red Bumps On The Breast?

Hi I just have a quick question. .. I have a small red bump on my nipple and it s sore all the time. It s happened before and I also have 2 or 3 red bumps on my other areola and nipple. I should get my period in a week or so and I didn t know if it was period related. Yes I m sexually active with my long time boyfriend but I don t believe I m pregnant