Breast tenderness is often one of the earliest signs that you are pregnant.  Soreness and sensitivity typically develop during the first trimester, as your hormone levels increase to prepare for feeding your baby.  During this time, you may feel uncomfortable in some of your regular activities like exercising and even sleeping. To ease discomfort try taking a warm soothing bath, covering breasts with cold or warm cloths and wear high quality cotton maternity bras.  Luckily the discomfort tends to pass by the second and third trimester.