I have learned to question and question and question again when something does not feel right. Does your Ped have any other Dr in the office? If so make an appointment with them and see what they say, if this persists and they can not answer you go to another practice.
As far as the drinking and eating. My lil one is who 17 months now, goes thru this at times. I give her Gatorade, as she does not like the pedialite and she would eat some apple sauce for me as well.
I know it is frustrating and hard, keep up the good work and don't feel bad about questioning the Dr or perusing a feeling you have as a mommy!