13yrs old had unprotected anal sex,didn't get period yet! help?

ok.. on june 2nd i had unprotected anal sex for like three minute's or less.. i was wet in my butt when we was doing it .and i was wet in my vaginal only because he fingered me ( sorry for explaining in details i know its nasty :S but i must get my point across) anyway its june 28 today and i didn't experience and pregnancy signs. and i want to know is my period late because im stressing. and if a "Sperm" was to slide down would i feel it? because i didn't feel anything slide down and go in my vaginal! so my question is do YOU think im pregnant. please be mature i know this is nasty but i really need help right now because i just wanna be a different person and study right now but i can't because im worried that my period is not here yet. an they say when your young your period is irregular. because in april i got my period around the 27 and also may. but other months they came around the 28 or 29. so like is my period switching? i made a HUGE mistake and i learned a lesson from this. all im asking is for advice i know what i did was sickening but it was a mistake and im not going to have any kind of sex til im more mature and responsible. that was my first and last time having sex. but i do have a lil bit ofstomache pains (almost like cramps) ,,what do you think that means..