My 8 year old son started vomiting yesterday, could not retain anyting, even juice or water, He complained of stomach pain, headache and fever. Today, he is no longer vomiting but still lethargic, still complains of headache, whole body pain, stomach pain. My younger daughter had the same symptoms 4 days ago and was better after 2 days. Whtat could it be? Please help, Many thanks.