Progesterone, which is the driving
hormone after ovulation, causes a slow-down in the digestive system. Taking progesterone can also cause an increase in constipation and abnormal bowel movements (been there, done that, but not IBS). Have you also thought about having yourself checked for endometriosis which can have an impact on bowel symptoms? That was my first indication of an endo problem, severe pain and constipation around my period.