What Causes Pain And Soreness In Breast With Spotting?

im 22 yrs old female... i had my last menstrual period on 25th of January and afterwards had unprotected sex... but my partner did not ejaculate in to me... i took i-pill the next day within 24 hrs... i again started bleeding on 12th february, with soreness of breast... bleeding lasted for 4 days... i thought i was pregnant and checked my Serum B HCG on 15th and it showed less than 1.2... i am still having the pain and soreness of the breast... what could it be?