Talk to Pediatrician on Throat Infection

Hi doc my son is 6 years old hos throat often gets sore, and he has a very bad cough. I have already taken him to the doctor and given him the prescribed medicines, but he doesn’t seem to get much relief. Now his throat is sore again, and he also has flu and a runny nose. This problem keeps coming back. Please advise what could be causing it and what treatment he needs.