Suggest Treatment For Vomiting, Loss Of Appetite, Diarrhea And Dehydration In Child

My 6 yr old grandson vomited at 3AM 5 days ago Saturday 3 am). Woke up and continued vomiting most of day with no appetite. Then the diarrhea started day 3 & he became dehydrated. Went to hospital had 1-1/2 bags IV fluid. Next day was more lethargic and vomited profusely & had 4 bouts of diarrhea. Very weak & will not sit up; walks crooked. Parents thought it was a bug & would pass but we are way past that. Perhaps appendix? It hurts him to urinate which he hardly does.