I Am A Woman And When I Do Any Type

I am a woman and when I do any type of aerobic exercise that gets my heart rate up on cycle days 10-19, I experience uterine cramping to the point I need to stop. The cramps are very intense. They go away after 5 minutes and then I can continue working out. I have normal 28 day menstral cycles. When I was on oral contraception, I never experienced this. What could be causing this? Someone suggested that it may have to do with vasopressin and low progesterone?