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Shaking is often a response to pain or to a fever. So, you should take his temp and see if it's elevated. Normal resting temp for a dog is 101-102.5. If it's elevated, you might be dealing with an infection and you will need to see the vet for possible antibiotics.
Until you can see the vet, I suggest that you switch him over to a bland diet of ONLY boiled chicken and white rice (no bones, no skin). Give him a tablespoon at a time until he shows improvement.
If you don't start to see this resolve, you will need to see the vet to rule out a parasite problem, giardia or coccidia. I would also be concerned about an intestinal obstruction.
Let me know if you still have questions.
You can also use boiled hamburger and rice if you have it. Don't fry it because the oil can upse the stomach. Just boil it and then wash away the grease.
You should see improvement within 24 hours if this is going to help. If it's a parasite problem, it will give shortlived relief but won't solve the problem.