What Causes Severe Pain In Abdomen Along With Nausea During Menstruation?

At night and in the morning for the past few days I have had this terrible feeling in my stomach that i can compare to a clenching fist.
I am currently on my cycle and this has been one of the worst periods I have experienced. BUT, this pain does not feel like cramps. I take birth control pills for the several years. And the day prior to me starting my period I finished up a 3 day pack of an off brand of Monistat. Last night was the first night of the past few days with this pain that I actually got nauseous and got sick. I have had a normal appetite and have not been eating anything differently.