Thanks guys--good idea Randi. Wish I had thought of it when I was at the vet! I may have some metrodinazole left over from not too long ago--I'll check.
The vet seemed to think it was a virus, though nothing serious appeared in the fecal stain. He checked his abdomen pretty thoroughly and Bentley showed no pain, and he didn't feel anything odd. He also did a rectal (Bentley was not a fan!) but said everything felt okay.
We were given the option of doing an x-ray for peace of mind, but decided to try the course of using some medicine. So he got a shot of Cerenia to stop the vomiting and is taking some metrodinazole as an antibiotic. If we don't see improvement by tomorrow, he'll got into the vet on Monday for an x-ray.
He has no lack of appetite and just ate a couple spoonfuls of chicken and rice. Oh, and the vet said he didn't seem too dehydrated, all good signs.
And Ann, thanks for the info. I have a friend who said her dog had a doggie flu type bug last month, so it definitely might be going around.