it might not be flu
. but your son needs to see doctor & needs evaluation for his symptoms soon. he will need some blood & urine tests with a chest xray if required. will have to rule out possibilty of enteric fever
or typhoid fever
. if he has travelled to some malaria
endemic area, possibility of malaria needs to be ruled out with blood tests. can start of cefixime
tablet 200 mg twice daily after blood test have been done as treatment for typhoid fever. subsequent treatmen & duration will be decided after reports of the blood investigation come.