Every time i take my metformin, i cramp&start bleeding, why?

Need more info: Cramps where? Bleeding where? Metformin can have side effects of abdominal pain and diarrhea. It usually does not cause menstrual cramps or bleeding, however it is commonly used in women with polycystic ovarian syndrome to help regulate their period and increase fertility. However, if you have not had a period in a long time, the periods can start irregular and heavier. See your doctor.