Dysfuntional Uterine Bleeding (DUB) is a common disorder of excessive uterine
bleeding affecting pre-menopausal women that is not due to pregnancy or any
recognizable uterine or systemic diseases. The underlying problem is
believed to be due to ovarian hormonal dysfunction. However, the exact
mechanisms remain unknown. DUB usually presents as heavy, prolonged, or
frequent bleeding of uterine origin.

In such cases, a visit to your gynecologist's office becomes in order - an ultrasound of the pelvis to make sure you do not have any tissue abnormalities, like a fibroid or a polyp, plus some routine lab tests, may be done.

many reasons can be the cause of that, but you really need to see your doctor.

On top of looking for the reason and correct it, bleeding for one month may cause anemia which should then be treated as well