I have been cycling on birth control pills since January, with no side-effects and no period. I am doing this because I have endometriosis and am trying to avoid pain and cysts related to that. I recently changed pills. I noticed some very slight monthly cramping. This week, however, I had spotting and finally, regular almost heavy bleeding. During the most painful point, I went to the toilet and passed some sort of tissue from my vagina. I assume it was some sort of uterine lining. Should I stop taking the pills?