You may have already tested for this, but has a urinalysis been done to check for a UTI? I say this because my dog went undiagnosed for months – he had/has many of the same symptoms yours does. Blood in vomit, lethargy, up all night in pain/distress, etc. Did do better on sucralfate. It was a UTI the whole time, he just didn’t show any of the classic symptoms like straining or dribbling pee/having accidents in the house. All other tests were normal. No one thought to do a urinalysis until he finally peed a bit of blood. (Yes, I am kicking myself.)
