A 32-year-old woman complains of amenorrhea since the delivery of a baby 15 months previously, despite the fact that she did not breastfeed her baby. The delivery was complicated by excessive hemorrhage that required a transfusion of 2.5 liters of blood. She has also been fatigued and has gained an additional 4.5Kg since the baby was born. Laboratory data show the following:Serum LH < 1 IU/L (normal, 4-24 IU/L)Serum estradiol 5 pg/mL (normal, 20 - 100 pg/mL)Serum TSH 0.1 mU/L (normal, 0.5 - 5 mU/L)Serum GH 3 ng/mL (normal, < 5 ng/mL)Serum ACTH 28 pg/mL (normal, 10 - 50 pg/mL)Serum prolactin 2 ng/mL (normal, Injection of 500 mg of TRH failed to produce the expected rise in both serum TSH and prolactin. Which of the following diagnoses most likely explains the findings in this patient?