I agree with DaGracer completely...that dog needs to see a vet right away!
My first thought when reading the symptoms was poisoning, but no matter what it is, I would STRONGLY recommend NOT trying to medicate him with anything until he's seen a vet. In trying to help him you could mask symptoms or make him worse.
You didn't give a lot of details (like how old he is, and what he was doing/eating before he became ill) but this site has a lot of information on what sort of foods/plants etc. are dangerous to dogs (and tiny dogs like yours don't need to have much to be effected). There might be something there that applies and can at least give you a place to start.
Veterinary Information - Toxins that Affect Dogs
Good luck with him...please write back and let us know how he is doing.