My daughter (3years old) becomes very pale after eating and looks very sick. Been going in for a few weeks.?

Needs a check. There can be digestive issues, metabolic issues, absorption issues, etc that can cause this. A thorough history by an experienced clinician can help solve this. There are many variables here that can lead to what is going on and what testing will help illustrate the problem. Get her seen and checked, and talk to somebody about it soon.
Needs Seen. Not sure but if after every feeding may be severe acid reflux.See your doctor.This is not normal!