A 35-year-old woman from Mumbai presents with 3 months of irregular, heavy, and prolonged menstrual bleeding. Cycles vary from 21 to 45 days, with bleeding lasting 8–10 days. She denies pelvic pain, dyspareunia, or postcoital bleeding. On examination, the uterus is normal in size and contour, with no adnexal masses. Pelvic ultrasound shows a normal uterus and ovaries with no structural abnormality. Endometrial thickness is 12 mm (measured in proliferative phase). Hemoglobin is 10.1 g/dL. Coagulation profile and thyroid function tests are normal. What is the most likely diagnosis?