A 30-year-old woman presents 2 months after a complicated delivery with massive postpartum hemorrhage requiring transfusion. She reports inability to lactate, fatigue, cold intolerance, and amenorrhea. Vital signs show BP 98/62, HR 58, temperature 36.1°C. She denies taking levothyroxine or other medications. Laboratory studies reveal TSH 8.2 mIU/L and free T4 0.8 ng/dL. Which of the following is the most likely diagnosis?

1. A)Sheehan syndromeGABARITO
2. B)Postpartum thyroiditis
3. C)Prolactinoma
4. D)Lymphocytic hypophysitis due to MEN 1
5. E)Primary ovarian insufficiency