Did you have your CA 125 levels checked? I have a 5cm complex cyst also and my ca125 is at 80. I am now very scared and going to a onc/gyn to have mine taken out.
It sounds like you have complex mass. Any complex mass has the possibility of being malignant. However, most do turn out to benign. Usually, surgery is required for complex masses that are over 5cm. Since it does have the possibility of being malignant, it is very important that you see a gynecologic oncologist. Your gyn should refer you to one for a consult. A gyn/onc can either assist your doctor during surgery or complete the surgery on his own. But, it is important that you have a gyn/oncs expertise in order to get the best outcome. Here are a couple of links to websites that have some information on the importance of an gyn/onc and will help you locate one in your area:
http://oreilly.com/medical/news/ovarian_ten_things.html
http://www.wcn.org/findadoctor/
There are many complex masses that are benign. Hopefully, this will be the case for you. Best wishes for a benign outcome and speedy recovery!