Anything can be wrong! Your dog could have gotten into something toxic or something he or she should not have, he or she could have a Blockage, the list goes on. It sounds to me, like it's time for a visit with the vet. Only a vet can diagnose and treat your dog. Shaking can be a sign of pain. Something may be causing your dog pain, which explains the shaking and whatever it is, it's also making your dog sick. Please don't let this continue. Take the poor thing to the vet, get it properly diagnosed and properly and effectively treated. The longer you let this go, the worse your dog will get and the harder it will be, to treat the problem.