My dog will not eat..?

We have tried every food possible, and have even mixed wet and dry food together which for a while he ate. Now he starves himself until he dry heaves/pukes up bile. The only thing he wants is people food, I've tried mixing certain people foods with his dog food that are supposed to be good for him but he either just licks it off or literally picks out every bit of whatever it is I put in there. I have also tried the dog gravy that doesn't work anymore either.