Get an appointment at a feeding clinic. There is one at Children's Hospital and at Kennedy Kreiger in Baltimore. My son has been at the feeding clinic at Childrens and was Failure to Thrive. He started at 14 months for an evaluation. He is now 4.5 and doing just great. We were also seen in the genetics and metabolic medicine area of Children's but my child does not have a metabolic issue. He does actually have a chromosome disorder, but that is unrelated to his eating disorder.
Childrens takes all insurance.
You don't give specifics of your child, but here is a yahoo group with a bunch of parents dealing with children with Infantile Anorexia, and eating disorder of young children
http://health.groups.yahoo.com/group/InfantileAnorexiaForum-OneBiteAtATime/
I am surprised that your pediatrician did not recommend a feeding clinic.