Coughing chihuahua -- please help

Our chihuahua, Ricky, could really use some help. He is a 2 1/2 year old neutered male who weighs 4lbs.

We thought that he had Kennel Cough, and it sounds just like it, but... it has lasted about 6 weeks, and none of our other dogs have gotten it.

Does anyone know what else it could be? He has been to the vet twice, was given Amoxicillin & cough tablets, but they did nothing. Neither has any over-the-counter cough medicine. Our poor little guy can't get any relief. He seems to do a tiny bit better sometimes, and then gos straight down hill again.

Other than the cough & gag, he eats fine, is alert & has no other symptoms. He is very tired from all of the coughing though.... and so are we! Nobody can sleep very well around here, and haven't been able to in 6 weeks.

Thank you.