Plus, he sounds all clogged up, like an old man or a Pug with a cough or cold. I’ve had his throat and chest X-rayed for stuck objects = nothing there.
I don’t know what that is, but if your vet can’t make progress, I would take Louis to a well-regarded teaching hospital. Our first Ridgeback had an illness that was referred to as “doggie aids”. They finally put him on steriods, which gave him an extra year of life. He lived to be 12.