I used to be on birth control... And I had surgery for polyps in my uterus about 6 months before I got RSD, and ever since I have RSD I am not regular at all. I never know when I am going to start but when I do. I am in bed for probably 4 days because its so excruciating. i am just glad I dont have it every month! I dont know if its the medicine that changes, but i do know that hormones change when you are in alot of pain...