What Causes Vomiting And Abdominal Discomfort In A 2 Year Old?

My 2 year old starting being ill 8 days ago, she would vomit anything including parecetomol after a few days she stopped drinking and we took her to er. No fever at all, checked for diabetes (negative). Tiny rashes around nuckles which go away. We have been giving her electrolites and paracetomol posterior. However, she is still very tired. She is ok when wakes up but by noon all wants to do is sleep. Curls up as if in a bit of stomach pain. Will spend most of rest of day napping, wake up for an hour and then want to go back to sleep. This is day 8, and has never been ill before 8 days ago. She moans alot and appears to have some sort of discomfort.