What Could Be Causing High Fever And Persistent Vomiting Despite Taking Calpol And ORS In A Toddler?

Hello Doctor, My son is 5 years weight 17 kg, he has been down with high temperature 101.8 , given him calpol yesterday and temperature was high today morning again so repeated calpol. He is vomiting everything he is taking even ors? What could be the reason and please suggest some effective medicine as I need to travel on Monday with him to another city. Thanks