I'm so sorry.
I remember your last thread and honestly felt that the vet was not being thorough enough. Reading this thread today I have the same thoughts on this internist.
I'm not sure why they have not hospialized him. They can figure out sone way to get the fluid dwn consistently even without a diagnosis. They should be able to do some imaging abd rule out tumors and then have some idea of what drugs to use.
IMO, PLE and PLN can be treated successfully in a lot of cases with immediate intervention. I think you should go to the Virginia Tech ER right now abd let them deal with this.