Reproductive Hormones - IBS occurs more than twice as frequently in women than in men and tends to follow a cyclic pattern, with aggravation during the postovulatory (progesterone-dominant) and premenstrual phases of the menstrual cycle3. Progesterone is known to delay gastric emptying and cause constipation; constipation with straining and the frequent passage of hard stools is a more prevalent IBS manifestation in women, especially during the postovulatory phase21. At the end of the postovulatory phase, the sudden withdrawal of progesterone that occurs with the start of the premenstrual phase may trigger increased bowel activity. Women frequently report loose stools and diarrhea before or with the onset of menstruation. In contrast to progesterone, estrogen has not been associated with exacerbations of IBS symptoms5,7. In one study, high levels of luteinizing hormone (LH) were found in women with IBS; drugs that decreased LH levels and consequently suppressed ovarian production of estrogen and progesterone resulted in significantly improved IBS symptoms22,23. LH is a reproductive hormone responsible for the production of testosterone in males and estrogen and progesterone in women. In men, the opposite result was found: low LH and low testosterone tended to be associated with IBS symptoms24. High LH therefore appears to cause exacerbations in women by stimulating progesterone and estrogen, yet have a protective effect in men.Along with progesterone levels in women, prostaglandins E2 and F2 alpha also increase in the premenstrual phase. Since they are powerful stimulants of bowel contractions, it is possible that women with IBS may have an exaggerated response to these prostaglandins3. http://altmedicine.about.com/library/weekly/aa010901b.htm
My symptoms are also now only monthly, I did always have gastro issues along with PMS even before I developed IBS, but now they are definitely IBS symptoms I suffer each month, along with the premenstrual cramping, etc.