Janet is a 33 year old female who presents with a 3 year history of infrequent periods and thinks she has had on average 6 periods over the last year. Her period is sometimes heavy and painful for the first 3 days of bleeding but she denies any intermenstrual bleeding, post coital bleeding or dysparenuia. She is up to date with her smear tests. She is able to manage painful periods with simple analgesia and would not have presented today had it not been that she and her husband have also been trying to conceive for the past 2 years but so far have been unsuccessful. She has a BMI of 33 and is a non-smoker. Systems review is otherwise normal. Pelvic, abdominal and thyroid examinations are unremarkable.
What is the most likely diagnosis?