The types of abnormal bleeding include excessive, frequent, irregular, and decreased bleeding. Excessive menstrual bleeding is a condition called Menorrhagia that can cause stress and severe cramping, among others. Irregular or frequent menstrual bleeding is a condition of Polymenorrhea and is often caused by STDs. Menstrual cycles at irregular intervals happen due to a condition of Metrorrhagia and can be caused due to infections in the uterus or birth control pills. A decrease in the menstrual flow is a condition of hypomenorrhea. It is caused by overactive thyroid function or kidney diseases.