From your history , your baby seems to be suffering from pneumonia
with the fever and chest pain
. What was the temperature like , was it more than 101 F (high grade fever). If high grade fever, there are other possibilities like upper respiratory tract
etc for which a blood work up needs to be done. His ENT work up is normal , so you can rule out an upper respiratory tract infection.
Apparently, you say the X ray is normal. What medication is your baby on now? Any antibiotics, antipyretics(for fever)? If you are saying he was delirious last night, I would suggest you take your baby to the paediatrician at the earliest. Any fast breathing , grunting, altered behaviour, shortness of breath
all are warning signs . Please visit your child's paediatrician immediately.
I hope your baby gets well soon :)