One of my dogs did this and we thought it was empty stomach too and we also did the Pepcid both of which helped BUT it was a squeaker in her stomach that was causing the trouble. We did a barium X-ray and the next day she was finally able to vomit it up. Good luck with your dog - hope it is something simple. Oh by the way it took 2 months and 3 vets to finally figure it out.
My first thought was a partial intestinal blockage. If completely blocked they will stop eating and even drinking, but a partial can go on quite a while. And, they won't normally act sick or as if in pain.
