WHY AM I BLEEDING??

i missed my period last month and i took an at home pregnancy test last week and it came back negitive so i figured id wait a few more days and take another one. yesterday at work i started have super SHARP pains, as if someome was stabbing me in the ovaries and twisting the knife. this morning when i woke up i was bleeding so heavily i had to buy overnight pads and ive been having to change them every hour or i bleed thru what im wearing. my periods are NEVER this bad and generally consist of light spotting and thats it. should i be worried?