Get your vet to check the length of his soft pallet, I had a dog that had breathing problems and it was down to her soft pallet, it done a lot of damage to her trachea and larynx and she needed to have a tracheotomy in. Very few get this bad so the sooner your vet checks this the better, he will be able to shorten it if it is too long.
This is Ellie’s story which may help you understand http://tracheotomy-in-dogs.yolasite.com/