D.W.
He could have an ear infection and have post nasal drip which can cause and ear infection. I would also get an air purifier for his bedroom. I spent about 35 bucks on one for my son and it does help. When you vacuum and dust it does stir up a lot of dust in the air. If you have a air purifier then it will get rid of the allergens in the air. Have you recently gotten any new pets? I would say more than a day,at his age take him to the doctor.