Almost Two Year Old Boy Has Had A High Fever

Almost two year old boy has had a high fever that no medicine is bringing down, vomiting will not eat or drink anything without gagging. He has blisters in his mouth & now has "foam" coming out of mouth while sleeping. Took him to er & strep was negative. They said it is just viral but I feel like something else is going on. It's been going on for 4 days now. It's only getting worse.