  urlLink DrWeil.com Article: Postpartum Depression : "Postpartum dysregulation of the thyroid gland has been considered as another possible cause of depression.
This condition is also linked to fatigue. The thyroid gland regulates several hormones and drops production dramatically after birth. It returns to normal functioning in three sequential stages. The first stage, which can last from 3 to 6 months, is hyperthyroidism where the thyroid goes into overdrive and results in anxiety and insomnia.
The second phase is hypothyroidism where production is slowed. During this phase a woman experience lethargy and weight gain. The final stage in recovery is when output reaches pre-pregnancy levels. Investigations into the relationship between thyroid dysregulation and postpartum depression have yielded contradictory results and no firm link between the two has been demonstrated. As a result, treatment is considered only when symptoms are severe enough to interfere with daily living. " 
