I'm sorry you're going thru this. I agree -- get a second opinion. That just sounds like too long.
Jackson has had kennel cough 2x now and it's a pain in the butt. I never got the vaccine for him due to reading it was unnecessary, etc, but we're constantly around other dogs, be it dog parks, pet stores, parks, etc, so he must have caught it from somewhere. So after he was put on antibiotics the cough cleared up in less than a week. Then we got the bordatella (up the nose). Well, I never updated the bordatella vaccine due to simply forgetting... and he got kennel cough again!
So from now on, I'm staying on top of it, as when he's had the shot it does seem to prevent it.