Poor Trooper! Sounds like he's having a rough go of it. It's got to be tough on you, too
It's so hard when they're sick and you don't know what's going on.
I thnk if it were our dog, we'd be making an appointment at the closest veterinary teaching hospital. Although pricey, the vets there tend to have a lot of experience with tough cases and can often pinpoint the problem where our regular vets cannot. Once you know what you're fighting, your regular vet can help with treatment.
If you think getting a second opinion this way is a good idea, talk to your vet about getting a referral--often times you can get an appointment faster that way.
Good luck with Trooper! I hope the vets can figure out what's going on with the little guy and find an effective treatment for him quickly!