Have you looked into giving your dog something more natural to help? My dog got KC before and the anti-biotics were not working for him, so I tried Respiratory Aid that is made by the Pet Wellbeing company, and it worked very fast! I keep a bottle in the cupboard just in case he has another flare up. Without sounding too much like an advert, this is what their website states about the product: Treating coughs and respiratory problems in dogs

Does your dog cough persistently, or have trouble breathing? It's likely he's suffering from kennel cough or a similar respiratory ailment.

Canine Respiratory Aid is an all-natural antibiotic, anti-inflammatory formulation. It safely yet effectively:

Soothes your dog's cough
Offers relief from respiratory conditions
Reduces breathing problems in short-nosed breeds
A dog's cough is never an illness in itself. Rather, it's a symptom of some other problem, like:

Allergies
Asthma
Bronchitis
Dog collar too tight
Irritants like cigarette smoke
Infectious disease (usually kennel cough)
Whatever the cause of your dog’s cough or breathing problems, Canine Respiratory Aid offers quick and safe relief.

What is kennel cough?

Many dogs suffer from kennel cough. This canine respiratory ailment is a highly contagious condition which – as its name implies – is common among dogs that spend a lot of time in close quarters: in kennels, dog shows, grooming salons, etc. Beyond causing respiratory problems, kennel cough can weaken your dog's immune system and make him more prone to catching other canine diseases.

You can help your dog avoid catching kennel cough (or other canine respiratory diseases) by not letting him share toys, food or water with other, unknown dogs. But if he does catch kennel cough, Canine Respiratory Aid will help ease the symptoms and help him fight the infection.

And, here is the link: Dog Cough Medicine - Respiratory Aid Treatment for Canine Cough and Breathing Problems

Samson is fine now, thank you! But if your vet doesn't give you anymore results I would try somewhere else. He could come down with pneumonia or something similiar. Maybe it's something to do with his throat?