I was told I have a 4.5 cenimeter ovarian cyst.. I have been on birth control for 16 years and have not had a period since Nov 1995. I have never been diagnosed with cyst before.. I actually went in for a pain in my side and hip and they found this...What is the chance it is functional?

Optional Information:
Female , Age: 30

Already Tried:
I have had an X-Ray, and a MRI and I am scheduled for a pelvic ultrasound