very drunk unprotected sex ...

I'm 15, and very stupid. On the 28th of December I had very drunk unprotected sex & he came inside me, me being stupid never done anything about it and just left it. About a week or so later i had a really sore back, i just thought it was because of the way i slept, which probably was a contributing factor, then recently i've been feeling more tired than usual but I am anaemic, so i suffer from tiredness regularly mostly during my period. I get my period on the 12th of every month and it's usually first thing in the morning, this morning i woke up, no period, but really bad cramps which lasted all day, when i got home from school i noticed a brownish colour streak in my knickers, assuming it was my period i just changed and added a pad but since then nothing, and usually my periods are very heavy which causes the anaemia, I also had a headache for about an hour yesterday & its very rarely I get headaches. Am i pregnant? is it possible to have spotting on the day your period is due?