Ok So My Last Period Was Around November 15 Not

ok so my last period was around november 15 not sure the real date but around then. i had unprotected sex on december 9 and it was only in for 1 minute at the most and he pulled out and jerked off and in ab 2 minutes he cummed. he told me he jerked off the previous night and he cummed and he said he peed at least 4 times between then . so today which is december 13 i was at school and i noticed this brown stuff come out then a few minutes later i went to pee and a ton of blood came out and got on my pants then i peed again when i got home and more blood came out it's a lot and it's normal color is just worried bc it's my first day of my period maybe it's light the first day i just don't understand why it's only when i pee am i pregnant?