Why am i getting my period bi-weekly? PLEASE HELP!?

For the past 7 weeks ive been getting my period bi-weekly!!?? It's like bright red blood! No cramps, bloating, or tenderness... I don't understand. It's not stress bec ive been under way more stress before and this never happened. I am not on birth control so it cant be that either. And I took a pregnancy test and im not pregnant!