Doctors or gyno girls, I need some help?

ok, well i'll make this simple....MY PERIOD ISN'T HERE!!! today is day 32 and nothing. and i took a pregnancy test and it said "not pregnany" so where is it? whats going on? i DO have cramps and stuff and im very irritable. (and when i had last time, it was up the backside...WHATS GOIN ON?)