Q. A 24-year-old female who gave birth 1 month ago presents to the emergency department complaining of fatigue, weakness and poor lactation. The patient reports she had heavy bleeding during delivery, which required a blood transfusion and a prolonged stay in the ICU. She also reports 10 kg of weight loss since delivery. On physical examination, the patient appears thin and pale. Her blood pressure is 70/40 mm Hg and her heart rate is 90/min. Assessment of her neck demonstrates no masses or thyromegaly. You note a lack of bilateral breast engorgement. Her remaining examination is unremarkable. What is the most likely diagnosis in this patient?