What Causes Period Like Cramps?

I am a 25 year old woman. I have been using birth control since I was 14. Over the years I have used many different kinds. In aug. 2007 I missed my period and it didn't return for 2 or 3 months. I took a home pregnancy test and it was negative. This happened again in Feb. 2009 for about the same time maybe a little longer. And it has happened again. My last period was in the middle of June. It took this third time for me to piece together that there is a pattern. The first two times I was using the NuvaRing and the third time I was using MicroEstrin. I assumed that what was happening was that I was having lapses in my ovulation due to how long I have been on birth control, but about 3 days ago I started having severe cramps. They are on both sides and so bad that a couple of times I have doubled over in pain. They are a little higher up that my typical period cramps which are generally very mild. I am worried that there is something wrong with my ovaries.....please help