A dog who usually eats well, then suddenly doesn't...is feeling ill. Either he is in pain, or has nausea or fever or everything. My bet is he's in some form of pain.
My thoughts on this are he needs to see a vet. I'd take him as soon as you can.
Took him and they started saying it was a hiatal hernia and then switch to a mass in his chest. They showed us the xray and there is something in his chest but really can't confirm one way or the other. They basically decided it was a mass and can do nothing. I am not super happy with that. Any thoughts on what we can do?
Where precisely, is the mass? In his esophagus, in his lungs, stomach? What did they say, -any more about this? That doesn't quite sound like a firm diagnosis to me. Did they do bloodwork? To see if he has tumor markers, that is if this mass is malignant, has it spread at all? Or examine his nearest lymph nodes?
It does of course depend on the location of this (tumor?)...if it is in a position where it is inoperable, then did they suggest any form of treatment...Prednisone? Radio-therapy? Chemo? Did they give any opinion as to whether this "mass" could be malignant or even possibly benign, but because of its location could be causing some blockage?
To my view, just telling you "it's a mass" and then sending you home with no solutions, no hopes, no treatment plan, nothing....doesn't seem quite right.
I would, if I were in your position, go for a second opinion, or ask your vet for a referral to a veterinary oncologist.