Recommended reading, some good ones to get started with:

 

Evaluation and Treatment of Postpartum Emotional Disorders, by Ann L. Dunnewold

Beyond the Blues, A Guide to Understanding and Treating Prenatal and Postpartum Depression by Shoshana S. Bennett, Ph.D., Ped Indman, Ed.D., MFT

Perinatal and Postpartum Mood Disorders Perspectives and Treatment Guide for the Health Care Practitioner by Susan Dowd Stone, Alexis E. Menken

Therapy and the Postpartum Woman: Notes on Healing Postpartum Depression for Clinicians and the Women Who Seek Their Help by Karen Kleiman

Cognitive Behavioral Therapy for Perinatal Distress by Amy Wenzel and Karen Kleiman