could be due to infection / gap in tympanic membrane. Get his ear examined by ENT doctor. Rupture of ear drum (tympanic membrane) may be due to foreign body in ear / pricking ear with ear buds or pointed objects, blow over head or sudden pressure changes. Middle ear infections could be another reason.
immediately as the fever
/ headache / vomiting
- are dangerous signs. However, the cause may be benign (like simple cough and cold - Flu) also.