What Causes Pain In Left Ovary?

Periodically, when I stretch, or laugh or even cough I have a painful feeling in my left ovary that feels like a charlie horse. it tightens about 30 seconds then spasms almost feels like something moving but I know I m not pregnant. I also have a lot of fullness in that area and it s tender. I m 14 months postpartum and had a c-section. Usually these spasms are followed by a period. Sometimes I have this happen 4 or more times a week, often times I ll have 2-3 periods a month I currently take a progesterone only birth control b/c I m breastfeeding