If menstruation continues for a month, clinically there may be several reasons: 1. endometrial lesions, such as cancer, endometrial hyperplasia or inflammation of the endometrium, may cause menstruation to last for a month. 2. may be caused by endocrine disorders. 3. may be caused by pregnancy. In this case, you should actively go to the hospital for examination, you can do routine blood tests, you can do sex hormone six tests, ultrasound, it is also recommended to draw blood to check the blood HCG, to exclude the possibility of pregnancy, according to the results of the examination clinical basically can make a preliminary diagnosis, according to the diagnosis and then give the corresponding treatment or do other disposition.