I forgot to add we have had high temperatures this year check he's not dehydrated, plenty of liquids. make sure hes using the bathroom regularly,if his urine seems dark he is dehydrated more than he should be .,get some pedilyte down him .
There have been many infection and virus going round this year not certain where you live but in the US one has been doing the rounds that last a week or two seems to clear up the reoccurs .Fever each time ,headache and some aching of limbs..if you scroll way down you will others similar ,my opinion is it takes it's course but if the child seems worse or you are really concerned take him back to the doctor . There was also another theory about more allergies than usual, does he play outside a lot ?