If he is not eating than nothing is going to come out. Is he still drinking? IS he lethargic? How is his attitude other than the vomit? If there are any changes I would get him to the vets.
Is it a hot day? On hot days my dogs do not eat as much. How old is he? Anything changed at all, his diet, excesize etc..?

Personally I have a 3 day rule, as long as they eat some, drink normal & act fine I give them 3 days till a vet visit (unless it is onbviouslly needed).
Hope he gets better!