You are having cough for 3 months , got relief after medicine , recurs .
Such type of recurring cough with impact on voice may be due to these possibilities , these include:
1 Allergic bronchitis
, diagnosis can be confirmed by physical examination by a physician . In this type of cough usually patient come in contact with some allergen like , dust , mite , mold , fine dusting powder , hay , fodder , smoke. These allergen produces antigen ,antibody reaction and causes bronchoconstriction
which produces cough as well as laryngeal irritation produces bad effect on vocal cord ( voice).
2 Asthmatic allergic bronchitis .
3 Laryngeal tuberculosis
, diagnosis can be confirmed by laryngoscope
In my opinion consult a pulmonologist
and get his opinion.