Dog stopped eating - no abnormalities at the vet.

I am really needing some quick help and support here regarding my dog! I have an 11yr old 55lb mixed breed named Dude. He is an extremely food driven dog but approx 3 wks ago his appetite has declined. Going from two meals a day to one then to a few treats then to nothing. Have been to two vets, had all blood work, parasite, worms, urine, feces, teeth/mouth, kidney, X-rays and full physical check by both vets. Temperature was fine, energy level normal, weight loss is definitely noticed now. The xray showed dilated large and small intestine and stomach with what they said was a large amount of gas but with no idea why so much more than normal or how to get it out. The xray showed no masses in his chest or stomach areas. They also found two small eggs in his feces but again not sure if it's related. (He is naturally a bit of a scrounge and will eat anything he finds that smells good)

They put him on a liquid to coat his stomach every 8 hours, omeprazole, metronidazole, broad spectrum dewormer and an appetite stimulant. Nothing has really changed other than the stimulant has allowed him to eat small amounts of chicken, beef, treats about an hour after taking it. He is drinking water normally. Not enough food to make up even one meal a day. How long can he go on with only small amounts of food? What do I do next? Possibly an ultrasound? Any ideas what else to look for? He is literally starving and my heart is broken. Can anyone help find an answer?