Gunky Cough

As already mentioned, I would make sure you get your carpets professionally cleaned if you haven't already to get rid of remaining pet hair/dander, and possibly have the air ducts cleaned in your home as well.

It's not milk and don't listen to anyone who says it is. If he's not allergic to it then that's not the cause. Honestly it does sound like allergies though. My husband has bad asthma and is severely allergic to cats and mildly dogs. He's had some very bad incidents through the years. Despite the fact that the pets have been gone for 6 months it can take years for pet dander to be totally cleaned. Have you had your carpets professionally cleaned? If not I would suggest a thorough cleaning of all carpets and upholstery. You may even consider getting a crew in to deep clean the whole house. My mother-in-law said she once got on hands and knees to clean every crack with bleach and a q-tip. Not my idea of fun. Also I have a mold allergy and wondered if he has more problems in colder weather. Never know. Good luck!

No milk will not cause excess mucus. It will cause it to be harder to clear when they have a cold or allergies. I would make sure that your son has plenty of water to drink during the day. That will thin out any mucus that may be draining into his throat. I have the same issues since I was his age and drink alot of water. I have had numerous allergy tests and have no allergies just a lot of drainage except when I am a dry climate. During the winter time dust from the furnance can collect and make drainage worse. Try running a humidifer in his room or the house that should help loosen and thickness of his drainage. Hopefully, he will out grow it. Also, did you know that if your child has mild allergies to cats/dogs that actually having them in the house will lessen his allergies overtime. Of course if he has major issues I would keep him away from all pets. If you haven't already I would suggest washing everything he comes in contact, professionally clean the carpet and furniture, change the furnance filters as pet dander can stay in the house for a long time. Also if you haven't changed your detergent it could be a mild reaction to that, try changing the soap and double rinse his clothes. Use liquid fabric softner and not the dryer towels as they leave a residue and can cause allergic reactions. I have one son, now 25, that it took a long time to figure out what was causing his allergy issues and it turned out to be my deodarant LOL. So I would keep trying different things until you figure it out. He still has issues to this day with things that contain perfurmed products but he says they are getting better but mold is a big one for him. Make sure that there isn't any hidden mold in the house. But I would say that since his allergy test can back negative for milk I wouldn't change anything but keep looking.

My condolences on giving up your pets. I know that can be difficult. I have a son with allergies/asthma, and we were fortunately able to make some accomodations that allowed us to keep our two dogs, but it was a close call. For some reason, cat allergies are usually more severe than allergies to dogs. It can take dog dander up to six months to be eliminated from the house once the pets are gone and up to 12 months for cat dander. You probably still have a significant amount of cat dander in the house if you had a cat. A pediatric chiropractor might be able to help with the mucus and drainage. They can do mild adjustments on children and tweak the sinuses. It's helped me quite a bit, and I used to be prone to sinus infections. Good luck.

Milk tends to thicken the mucus is the general reason to drink less of it. Maybe try a soy fortified drink as test.
The pediatrician or a pediatric nutrusionist might have some suggestions you should ask them also. Is there a pet in the house? Is the floor carpeted or hardwood/laminate?
Is there standing or wet areas in the lower level that mold could be issue if others also have the similar issues even more likely. When does the mucus get worst and when better is good to try to track the days, frequency, season changes and time. Is the child's nose stuffy most of the time?
There are saline sprays that could help thin the mucus.
My child who is 9 now was tested for most of the possible allergans by a specialist and game out negative for all of them! Yet he said well maybe the child has allergic like symptom due to temperature chanage and wind changes so the child who is older takes daily an OTC Allergy medicine anyway to help and it does.

My oldest went through this last winter and her cough lasted 6 months. We tracked data on it and sometimes it was induced by exercise or activity, but other times she would cough while she was reading a book or in her sleep. Her cough lasted 6 months, sometimes causing her to vomit. On two occasions she even stopped breathing and turned blue. Drs. thought it was asthma, but the inhaler and steroids did not change the cough. She was tested for every allergy under the sun and her test results came back clean. She had 3 chest x-rays in one year and everything came back fine. In the end, the pediatric pulmonary specialist told us that her lungs were immature and underdeveloped, simply due to her age, and just needed time to learn how to breathe. In the spring, her cough stopped just as suddenly as it started and we haven't seen anything like it this winter.

Could it be from his sinuses instead? Maybe some mucus that's draining from his sinuses and causing the cough? I have that problem at times (allergy to dust mites), and it is especially bad when I have a sinus infection (which I don't think he has). Maybe he's just a bit dehydrated, too, since it is winter. Try increasing how much water he is drinking and try to keep things well vacuumed and dusted and see if it helps.