The cause of 'postpartum blues' is:
Decreased estrogen
Decreased progesterone
Increased prolactin
Decreased estrogen and progesterone
Puerperal Blues/3 Days Blues/Baby Blues

It is transient state of mental illness observed 4–5 days after delivery in nearly 50% of postpartum women.
Postpartum blues occurs at the height of hormonal changes. 
Patients present with depression, anxiety, fearfulness, insomnia, helplessness and negative feelings towards infant.
It may last from a few days to 2–3 weeks.
Generally self limited, 20% of women may develop depression in the first postpartum year.

Treatment: Reassurance and psychological support of family members.
Post-partum Depression

It is observed in 10-20% of mothers.
It is more gradual in onset over the first 4-6 months following delivery or abortion.
Changes in hypothalamo-pituitary-adrenal axis may be a cause.
Manifested by loss of energy and appetite, insomnia, social withdrawal, irritability and even suicidal attitude.
Risk of recurrence 50-100% in subsequent pregnancies.

Treatment: Should be started early. Fluoxetine or paroxetine is effective and has fewer side effects. According to kaplan, the cause of postpartum blues is :
“The sudden decrease in estrogen and progesterone immediately after delivery may also contribute to the disorder, but treatment with these hormones are not effective.”