My Son Has Been Clearing His Throat Coughing Clear Mucus

My son has been clearing his throat coughing clear mucus for over 5 months. Every few minutes he is clearing throat to spit mucus. He carries a jar around with him. Also interrupts his sleeping. Has been to doctor several times and told its sinus, or chronic congestion. No doctor has examined mucus, or xray performed. Mucus now very smelly.