If it's really bad he might need to get a course of antibiotics such as amoxycilin but only if the infection has reached his chest and taken over it completely. Usually if one lung is infected, by beating each side of his chest you will notice that one lung has a deeper sound, the doc will probably do this with his stethiscope whilst asking him to take deep breaths and prescribe antibiotics but these should only be taken as a last resort as they deplete your immune system.