high fever, coughing, viomiting can be related to viral fever viral fever tend to be higher and shitter duration Also to increase in throat symptoms make his problem worse however generally viral fever tend to be self remitting As your child is tested for certain illness and found to be negative then it is most likely some viral fever only. In my opinion best course would be proper rest, paracetamol, gargling with Luke warm water and healthy diet. most of household tend to give hot chicken soup or veg soup to children in these fevers and actually it s helpful Be watchful for any worsening of fever, any altered behavior, problems of breathing and if child feel too I ll. In all that scenario rush to nearest hospital I am giving this opinion based on information you provided but I will suggest if you feel that child is not improving please do visit your doctor . wishing him luck