What Causes Persistent Fever Along With Swollen Cheeks In An Infant?

My grandson has had the flu for 5 days. He has seen the doctor and the doctor was not alarmed. He responds to baby Advil, but when it wears off the fever is back and his cheeks are swollen. He has had all his shots...he's 20 months old. He has also been teething since a few months old and has all his teeth except for a few molars. Any thoughts??