There are many possible causes of heavy menstrual bleeding, such as a change of hormonal balance, fibroids and polyps, infections or bleeding disorders.
Fibroids and polyps
Fibroids are mostly benign (non-progressive) tumours in the uterus, while polyps are incidents of endometrial overgrowth. Both can cause heavy menstrual bleeding, and may be removed if they are causing problems.
Infections of the uterus or cervix can be serious and include excessive blood loss. Infections are generally treated with antibiotics.
Abnormalities in blood coagulation (thickening of blood for blood loss to slow or stop) are serious disorders and medical treatment is necessary. If you think this is something you suffer from, speak to your doctor as soon as possible.