Hello and thanks for writing in at HCM
In my opinion you needs to give a course of antibiotic to your child with plenty of water and electrolyte or ORS
powder. Keep him hydrated by giving boiled or RO filtered water. If he vomits after giving water or medication than take him to ER and get i.v. administration of fluid and antibiotics. Keep a watch on urine output. If urine is less or stopped than immediately rush to the ER.
Best Wishes and get well soon