A 28-year-old woman presents with a 6-month history of irregular menstrual cycles ranging from 24 to 45 days. She reports normal flow, no dysmenorrhea, and denies any systemic symptoms. On examination, she is normotensive, BMI 22 kg/m², with no hirsutism or acne. Pelvic ultrasound shows normal ovaries without polycystic morphology. TSH and prolactin are normal. What is the most appropriate next step in management?