What Causes Pink Discharge Before Periods?

I'm 20 years old, 5'8", 145 lbs. I had my last menstration cycle July 8th. For the past two days, whenever I urinae, there is a very very light pink/ red/ drop of blood on the toilet paper. It does not hurt/burn/itch etc. to pee. However, my boyfriend came into town 2 weeks ago and we have unprotected sex, and he occasionally ejaculates inside. We have done this in the past while i was on/off birth control pills, but i have never been pregnant. Is there a connection to the light bleeding even though my period is not due for another week?