My Kid Is 3 Years Old And He Strtd School

My kid is 3 years old and he strtd school in january. Since january his chest is not getting clear and his cough is not going. We have given all medicines presribed by dr. But cough gets finish for some time then after few days it comes again. I really dnt undrstnd what should i do. M in uae right now and giving mucolyte syrup 3 times a day(5ml)