Hi welcome to HCM... Such a long duration cough could be from tuberculosis but according to history x ray is clear.... Cardiac cause should be ruled out as they can lead chronic cough ... For that EKG done ... Second sputum cytology examination also can be useful.... Cough can be neurogenic also ... Get your stool examination to rule out parasitic causes .... If needed stool culrur done ... If no significant cause found than problem can be functional.... Your detail history and examination needed to decide what work up is to be done For excess troublesome dry cough dextromethorphan can be given ... Advise ; pulmonologist consultation for examination Take care