Not read all the replies (kids are rioting around me, so typing with speed), but have you investigated possibility of eosiniphilic eosophigitis? It's symptom-free sometimes, more common that you'd (or your MD) might think, and leading sign in kids is poor weight gain. My DS being investigated for it. He's BF but I'm also supplementing him with neocate. Hideously expensive but a scheme here in BC, Canada, pays for it (thank goodness).
1/10/10 at 10:55pm