[mojo]

I had a very similar thing with my dog. She wouldn't eat - I too thought she was being picky, didn't want her dog food, just wanted people food, etc. She became lethargic, depressed. When I noticed the weight loss, I took her in. Took vet forever to diagnose and figure out what was wrong with her (addisons disease).
Point is, your dog clearly seems ill. If your vet doesn't seem concerned or can't figure it out, I would find another vet. Not eating is not normal and something is wrong.
Sorry you are going through this.