My dog is wasting away before my eyes...

[wickett]

My dog is eating dirt, rocks, wood, etc. I feed him but it's like he's starving. He throws up everyday. He was throwing up bile for a couple YEARS every morning, now it's like dirt. I've been taking him to the vet for the last three years for being sick, but in the last year he has lost 25 to 30lbs. (he'a a retriever) I love him so much and I don't know what to do. The vet and has run many tests, but can't figure out what's wrong with him. His spirit seems pretty good, but he's getting weaker and weaker. I don't know what to do...