Excessive Mucous in Child

Its been a few years since ive tried to treat my son with his colds, as Ive had no success with homeopathy on him and gave up. Im hoping to try again. Heres his story.

6 years old, blonde hair, green eyes, skinny build, doesnt like to eat food. Likes to drink milk instead. Very loveable and cuddly one on one, but doesnt play well with others and doesnt respect peoples personal pace. When at school he will walk into group of playing children and disrupt their games. Wants to be the boss and has to make all the rules. Very few friends his age because of this. Very smart, but temper is a big issue with him.

This is his main issue I need help with. When he gets a cold it starts in his head. Tons of mucous out his nose and it then turns to post nasal drip.Mucous starts clear and then thickens up some and turns bright yellow. He will cough non stop for days and cant sleep. Ive resorted to over the counter remedies as nothing natural has been abe to help stop the mucous flow. Even tonight he is coughing constantly and is very uneasy with this. Its a choking cough and its almost to the point where I think he will throw up with each cough. Even the over the counter prescriptions wont slow the mucous down tonight. Years ago a dose of Nat Mur worked amaing for him but it only ever worked once, nothing else has touched it. Any advise either homeopathically or any other great natural remedy would be greatly appreciated.
thanks so much.