Dermoid cyst recurrence after surgical removal of grapefuit sized cyst and 90% of ovary??

I had most of my left ovary removed last summer due to a large dermoid cyst.  I just came from an ultrasound and the tech mentioned that their was a small cyst on the right ovary and the left cyst was still pretty big.  I almost fell over.  What left one?  I had my left ovary removed and a cyst.  Apparently it is back or something new is back on that measly little ovary.  Also, my periods strangely stopped about 6 months ago with no real menopause symptoms.  I am 47.  Any ideas on dermoid recurrence??