Reasons for premenstrual constipation
Progesterone is usually to blame for constipation before your period. Levels of this particular hormone spike before the onset of monthly menstruation, and it slows down the digestive system.
Immediately after ovulation, progesterone (which is a natural muscle relaxant) drastically increases. This essentially leads to constipation by delaying the movement of food through the bowels.
Thankfully, PMS constipation typically gets better once menstruation actually begins. This is a direct result of a rapid drop in progesterone levels during your period. Some people experience temporary diarrhea when this happens, since the hormone previously responsible for slowing down the digestive system is suddenly absent.
Another contributing factor for PMS diarrhea is a sudden boost of prostaglandins — a hormone-like substance produced by the endometrial cells. If present in extremely large amounts, prostaglandins may find their way into the muscles lining the bowels. While there, they encourage the intestines to contract and move the bowels very quickly.