My dog is shaking uncontrollably, it is not seizures....?

HI. I took my dogs to the vet three days ago. My Bison was healthy. He got a corto short for allergies, a negative fecal exam, nails cut, glands popped, and an antihystamine for hair loss. He was on this med. once before. He has since been shaking uncontrollably. Like he is shivering, or trembling. He is playing hard, eating and drinking. After the $500 bill at the vet the other day, i don't want to go back. I called them, they said those are not side effects of the med. i told them that i discontinued the med last night anyway. They said to watch him, and bring him in two days if it continues. That was the secretarty that gave that info.... i don't think it is good enough or accurate.... what could this be....????? thanks in advance.