I don't know if your vet has considered that he might have aspirated a foreign body? If so, he will cough and cough, might have ups and downs, and might cough up blood. He could also get a pneumonia behind what he aspirated, so he might have a fever and secretions. It wouldn't explain the eye goo you mentioned in your first post.

The way to make the diagnosis is to do a bronchoscopy--if you do this, it should be done by a specialty vet who has experience (and equipment) with the technique. Dogs have large trachea's compared with humans, so its not really very risky, but if he has something down there he won't get better until it gets out. Its also possible that he had aspirated something and he coughed it out, and now his trachea is scratched up (he may still cough with this)--steroids should help the swelling if this is the case.

Good luck.

Jakes mom