My dog wants to vomit but can't. How can I help?

[Tammy L]

My dog is sick and he wants to vomit. I took him to the vet already so don't say that again. The vet said if he barfed again then he has to go overnight but he didn't. He barfed once and he isn't active at all. Please Help.

[Suzi-Q]

I'd be calling my vet back...