Did he eat today? Did food come up or is it just dry heaves?
Shelby gets an upset tummy if she has a naughty day of eating carpet, cobwebs and floor crumbs
(Sounds like my house is filthy) She vomits up bile and one day she had dry heaves.
I have found that getting something in her tummy first thing in the morning helps. If Joey won't eat dog food, try a little baby rice cereal and see how that sits with him.
I am not a vet though. Please don't take this as expert advice. Just a mommy that has been there and done that.