Suggest Treatment For Cough And Congestion

My son is constantly clearing his throat when he breathes out. He hardly swallows at all. All he does are these little coughs, sometimes one bigger one and sometimes about five little ones in a row. It is continuous, all day for about two and a half weeks now. It s worrisome. He did it before and one day he just wasn t doing it anymore. That was back in October and didn t do again until, as I said, about two and a half weeks ago. I took him to the doctor four times back in October and his throat was fine every time and they said it was probably post nasal drip or just a habit/tick for the age. He does it when he s sitting or active...it doesn t change.