My Son Of 11 Year Have Cough I Took Him

my son of 11 year have cough i took him to doctor after few days he was OK but doctor continue his medicines (antibiotics and others ) for many days by saying the infections is stil here now he took antibiotics and cough syrups for above 1 month now he is ok but some times he ha s little cough (1-2 times) . I don't under stand what should I do to cope up the effects of long course of antibiotics