Hi,
Ovarian cysts are pretty common, since you had it during a child-bearing age, then the odds of cancer would be small.
What is unclear would be the symptoms you mentioned that are still present. If this is regarding pain (especially if your doctor sees no clear reason for this), then this may be enough reason to perform diagnostic testing. The simplest testing may be a repeat sonogram. From what you've posted - there are no alarming features that should make the testing focused primarily on investigating the possibility of cancer.
You may want to find out your baseline risk for ovarian cancer per se. You could check out this link to help you estimate the risk.
http://www.yourdiseaserisk.siteman.wustl.edu/hccpquiz.pl?lang=english&func=start&quiz=ovarian
Based on this, you could discuss about screening options. Bear in mind though that screening is not routinely recommended as the appropriate strategy has not been clearly defined.
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