Janet is a 33 year old female who has a 3 year history of infrequent periods, around 6 periods on average a year. Her period is sometimes heavy and painful for the first 3 days but she denies any intermenstrual bleeding, post coital bleeding or dysparenuia. She is up to date with her smear tests. She and her husband have been trying to conceive for the past 2 years but so far have been unsuccessful. Systems review is otherwise normal. Pelvic, abdominal and thyroid examinations are unremarkable. Her BMI is 33.
What is the most likely diagnosis?