TMI! light bleeding.

I don't have pictures but I've had sex with my boyfriend on 3 different occasions and afterwards I'd go to the bathroom and wipe and there would be a light tinge of blood on the tissue! What does that mean? This has all been in one week. My period is due in 3 days but this never happened. I also have tender breast and mild cramping which I believe is just because my period is coming. Do you guys have any idea about the pink stuff?