Hi there. What you are describing is him bringing up something called 'bile' that is secreted by the stomach. If he hasn't eaten, yet is vomiting, this is not a good sign. If he can't keep oral fluids down then he needs to see a vet today. The key to getting water to stay down when the stomach is inflamed is to offer very small amounts frequently, so 2tbsp every 15-20mins, any more may stretch the stomach and cause vomiting.You can add 1tsp sugar or glucose, a pinch of salt and a pinch of bicarb to a pint of water as a rehydration supplement. I would worry that the shaking is due to either a lack of glucose(sugar) in his system, or dehydration. You should ring the vet and get an appointment as soon as possible in case he has a blockage somewhere in his intestinal tract, or a nasty infection. In the mean time keep him warm and offer the small amounts of fluid, often.

Andrea