Differential Diagnosis for a 35-year-old Postpartum Woman with Depressed Mood and Fatigue

Postpartum Depression (PPD): Given the patient's history of giving birth 14 months ago and symptoms of depressed mood and fatigue for the past six months, PPD is a strong consideration. Although PPD typically presents within the first year after childbirth, it can sometimes be diagnosed later.

Anemia: Fatigue is a common symptom of anemia, which can occur in postpartum women due to blood loss during delivery or poor iron intake. Breastfeeding can also contribute to anemia if the mother's diet is deficient in iron.
Hypothyroidism: This condition can cause fatigue, depression, and other symptoms similar to those experienced by the patient. It is more common in women and can be triggered by pregnancy and childbirth.
Sleep Deprivation: Caring for a newborn can lead to significant sleep deprivation, which can cause fatigue, mood disturbances, and decreased cognitive function.

Postpartum Psychosis: Although less common than PPD, postpartum psychosis is a severe and potentially life-threatening condition that requires immediate attention. Symptoms can include extreme mood swings, hallucinations, and delusions.
Pituitary Apoplexy or Sheehan Syndrome: These rare but potentially life-threatening conditions can occur in postpartum women and cause symptoms such as fatigue, depression, and hormonal imbalances.
Underlying Chronic Medical Condition: Conditions like diabetes, chronic kidney disease, or heart disease can cause fatigue and depression and may have been undiagnosed or unmanaged during pregnancy.

Postpartum Autoimmune Disorders: Conditions like postpartum thyroiditis or autoimmune hemolytic anemia are rare but can cause significant morbidity if not recognized and treated.
Nutritional Deficiencies: Deficiencies in vitamins like B12 or folate can cause fatigue, depression, and other neurological symptoms, especially in breastfeeding women with poor dietary intake.