What Causes Nausea, Vomiting And Dizziness In A Child Post Food Intake?

My daughter has recently started waking up in the morning and about 20 min. after eating breakfast she gets nauseated, throws up, shakiness, and dizziness. Her doctor thought maybe acid reflux but the Nexium has not helped and now it is also happening throughout the day. Her face looks paler than usual and she has had some blurry vision as well as increased hunger and thirst.