I get painful bladder spasms every month one week after my period normally late evening. not sure why or what can i do to stop it happening?

?endometriosis: Interstitial cystitis is a chronic pain condition of the bladder and can also cause pelvic pain and urinary symptoms similar to endometriosis. Bladder endometriosis occurs when endometrial-like cells grow on or through the walls of the bladder. Diagnosis may require cystoscopy with biopsy and or laparoscopy with biopsy. See your gynecologist for more information