A 35-year-old woman, gravida 3, para 0, aborta 3, presents with her male partner because she has been unable to conceive despite trying for more than 1 year. Her menstrual cycles have been absent for 9 months, and she has occasional mild cyclic pain. She has a medical history of 3 suction curettages. Her BMI is 24. Investigation results are as follows:
Hysterosalpingogram: Obliterated uterine cavity, no tubal dye spill
Progesterone (midluteal): 48.0 nmol/L (16.4–59.0)
Partner's semen: All parameters normal
Which one of the following is the most likely diagnosis?