What Causes Menstruation Cycles To Happen Every Two Weeks?

I recently had a pap in March and it was normal. I also had test that said blood, hormones and everything was normal...I was on depo provera for 2 yrs. but got off of it in June of last year. In April I started getting my cycles every 2 weeks, is that normal? I dont want to be put on birth control because I am trying for a baby.