What Causes Distended Abdomen And Constipation In An Infant?

my baby is just one and half month old and he is having problem with passing stool,which is resulting into stomach destention..he passed his first stool after three days of birth with the help of pipe..but after five days he seemed alright he could pass stool on his own till couple of days back he had the same problem...he also vomited some green stuff in his second day of birth ..we have done his biopsy test which stated..section shown rectal muscosa and muscularis mucosae.there are few nerves,but no ganglion cells are seen..please correlate clinically and follow up...what do you suggest is the best for my baby..