What Causes A Delayed Period, Stomach Pains, Cramps After Unprotected Intercourse?

i had unprotected sex with someone about 3 weeks ago. he didn't let anything in me because i let him do it for a few minutes. i was supposed to get my period the first week of february but never got it. i took the pregnancy test 3 times this week. and it was negative all 3 times. i have pains in my tummy like cramps but no period. i still havnt gotten my period whats wrong with me??