Im on the birth control shot so i dont have a period but a wk ago i had sex & he didnt pull out am i pregnant?

My stomach been cramping and ive had some diarrhea and i been feeling nausea for last couple of days and i also took a pregnancy test and it came back negative but im still confused. But even if I'am pregnant i cant remember the last time i had a period. What should I do.?????