RSir, My Child Of 19 Months Always Have Upper Respiratory

RSir, my child of 19 months always have upper respiratory infection and cos of that he takes antibiotics almost every month. Whenever it attacks, his breathing changes. Last month he was treated of pneumonia and this month he just finished another antibiotics cos of the breathing and sudden cough. Pls, what should I do? What could be the cause? Tnx.