What Causes Popped Feeling In Stomach With Two Periods In A Month?

I have had my period twice a month for the past few months with stomach pain, nausea and also occassional vomitting. Felt very tired and before double periods started for me, my original period was a few days late. Then i felt a popped feeling inside my stomach like i had pulled a muscle. I had gotten my period. Now it's been 2 in one month. I went to my obgyn after speaking with the nurse who told me she suspected a ruptuered cyst. At dr. appt, dr also said she believed it to be ruptured cyst, sent me for ultrasound. Tech doing both internal and external ultrasound said it may have been a ruptured cyst but she had seen no signs. My obgyn's office at this time still has not called me back after 2 1/2 wks with results nor to schedule other tests. I am frustrated bc i don't know what is going on with my body. I am almost 28yrs old, had two children, 2 misscarriages and now two periods in one month. Actually just had my last one start Nov.30th, end Dec. 4th and now started again today. My periods used to last 7 days but only happened once a month. I am not on birth control and haven't been since feb.2011 with regular 7 day periods. Irregular periods started in sep. If you can help me with some answers that would be great!