High CRP and fever. And infection?

My son got gastroenteritis two weeks back, with loose motion, vomitting, and high fever. His blood parameters were ok, but CRP was around 200. Got admitted in a hospital, got treatment and all symptoms subsided and got discharged after 5 days, with antibiotic prescribed for 3 days. Again on the 4th day night, he developed mild fever and is persistent for almost 7 days with mild fever. Dengue , typhoid, malaria all negative. Again CRP is 42. No other pain, vomiting symptoms except mild fever( around 100.5) every 7 hours. Today is 7 th day and antibiotic taxim is started orally. Otherwise he is active, he is eating, sleeping and playing. What could be the reason? Previous infection or any new infection? How to control the inflammation and infection? Is it a serious issue.?