Baby blues is the what professionals call the emotions (tearfulness, moodiness, exhaustion) that commonly occur after childbirth. This "non-disorder" affects 60-80% of new mothers and typically peaks within 3-5 days of delivery. It usually resolves on its own within 2 weeks. It is thought to be the result of the extreme hormone fluctuations that occur during birth and may be related to sleep deprivation.
You can find more information about postpartum depression here.
While the baby blues typically resolve without treatment, there are things that new mothers can do to address the symptoms: