Hormones are involved in the inflammation and pain responses during our menstruation cycle. They reside in the uterine lining when shed. Once released, they increase the force of the contractions during the first couple days of your period. If hormones are healthy and balanced, the affects of shedding the lining will not be painful. However if hormones are not balanced, the more severe the cramping is.
Very severe symptoms can also cause nausea and diarrhea.