What Causes A Prolonged Menstrual Period And Abdominal Pain?

I had my period for almost 4 weeks straight. My bloodwork came back normal. I went for an ultrasound the other day (takes a week to get the results) and the technician could not find my left ovary because of "shadows". How can they not find an ovary?? Also this is where the pain has been that i've been having that has radiated to my back. I'm just worried and wondering if there are any suggestions on what it could be. Thanks.