7 months kid persistent cough. Issues.

My son is almost 7 months now, he is super active and playful. Normal hight weight and looks healthy. he started coughing when he was 4.5 months, which looked like fake coughing but increased bit over the time. After 15 days We visited pediatrician who checked and said all good. 15 days passed and he devloped high fever & infection. Had chest xray, dr told LRT infection in lungs, got hospitalized for 2 days & treated with antibiotics. Post 15 days, He still do coughing manu times a day , again dr said he is all good as he is playful and didn't cough infront of the dr. Few days passed but he is still coughing, and devloped fever when we got him for outing. We r so tensed that what exactly cauing it and our son doesn't have any other lung issues.