MSRA-2712

A 19-year-old female patient presents to the GP surgery with a 2-year history of heavy menstrual bleeding. She reports that it has been manageable since the start of her menarche at the age of 14 but last 2 years it has become increasingly heavy that it has been causing problems at college. She has to change the sanitary towels every hour on the first 3 days of her periods and has been experiencing significant social embarrassment associated with over-flowing. She reports mild cramping pain on the first 2 days of the menstruation and denies dyspareunia. She is currently not sexually active. You arrange some blood tests which showed a mild iron deficiency anaemia but otherwise normal. An ultrasound revealed a normal looking uterus.
What is the most likely diagnosis?