Pack is azithromycin
is clarithromycin-both are antibiotics with almost similar action.
As the chest ray is negative,you need not worry as cough from most of the viral infections take time.
In post viral state therecan bevwheezing which can result in cough especially at nights your doctor can disgnose it by examining the child.
Mitral valve prolapse
is usually a symptomatic in children-depends on the hemodynamics in echo report whether there is severe mitral regurgitation