I am 19. 5 3 and 120 lbs. Every month, once a month for an hour I get severely painful diarrhea. This pain is so bad that I can barely move, and I cannot go through it again. My doctors are convinced it s endometriosis, though we have no proof. I m convinced it may be something else, but I have no idea as to what. I am lactose intolerant, so I avoid dairy. I ve been the same height and weight for 4+ years. I have no other issues besides gastrointestinal.