The most common cause of unusually slow weight gain after the first few weeks or months is that the mother's milk supply has decreased. (breastfeedingmums.com)
Daily consumption of alcohol has been shown in the research to increase the risk for slow weight gain in the infant. (kellymom.com)
The reasons for the weight loss are myriad; I'll focus here on the most common reason given for slow weight gain: low (or insufficient) milk supply. (rivertownmamas.com)