I think I may have the same thing! I have painful periods and a nagging sharp pain below my belly button, I also get some nausea. I told my doctor and he said he's going to send me for some tests if the pain isn't gone in two days (I doubt it will be). Hopefully I'll be able to have the cyst removed!
As for the anxiety, do try not to worry about it especially now that a doctor has seen it. If there was any doubt, it would be biopsied immediately. Some cysts take months to go away, if your symptoms suddenly get worse then go back to your doctor, they'll probably remove it for you if it''s causing you great discomfort