me and my boyfriend had sex last sunday. while doin that he was tryin to get in me to sudden that i felt that im not lubricated that well. 3 days after that i noticed that i have a reddish to brownish spot on my undies. the spotting lasted for about 3 days? im expecting my period on the 16th of march. im confused if it was implantation bleeding, abrasion from intercourse or just my period. please help me to understand, what's really goin on.. im so bothered..