I have a dull pain in the left hand side of my pelvic area that occurs 1 week after my period each month. Its like period pain but only in one side. There are no other symptoms, and the pain generally will only last 3-4 hours on that day only. Any ideas?? Ive had an ultra sound that revealed I had a retroverted uterus but no no cysts on my ovaries. What could be causing this pain??