pregnancy or period symptoms? help!!

My boyfriend and i had sex a week before my period, so, we made it the 29 of sep, but he only enter it for a few second and then took it out, then he came out side. I was expecting it the 6 of oct (i have a 28 day cycle) but all i received that day was a brown discharge that goes on and off. Im at my second day my original period hasn't come yet, And i need help knowing what is happening (im 16, and scared to tell my mom)