Actually, I am in that position right now. I have a 2.9cm cyst on my left ovary, and I went for an ultrasound, and blood test for a pregnancy, and it was negative. I have never been pregnant in my life. The last period I had was August 21st. I still haven't gotten it yet.
an ovarian cyst is common and if it is a corpus luteum cyst that hasn't gone away since ovulation that it is causing your progesterone levels to remain too high for your period to come even though you are not PG. i would see the doc to get treatment and once the cyst goes down the progesterone levels will drop and your period will come. this is very common and will go away with time. i hope this helps.
love....kimmie