Can An Ovary Cyst Cause Amenorrhea?

I originally started my period about 4 years ago. My period got fairly regular up until last year in December. I had it for 2 months non-stop. I went to the doctor then and they found a sist on one on my overies. It went away and was regular again. However, I haven't had my period since mid-July. It's been 4 months. I am a virgin so I know I am not pregnant. I haven't changed eating habits since then, nor has my stress level changed. What is wrong with me?