Hi, I am Dr. Peter and would like to help.
1- Any vomiting or diarrhea?
2- Is he lethargic?
3- Take a look at his gums and see if they are pink like yours or pale?
4- Can you take a rectal temperature?
The symptoms your dog is exhibiting are very non specific. It is common after a rabies vaccine for dogs to be more quiet for a day or two. But, what you are describing appears to be more than just due to the rabies vaccine. You need to speak to your vet to do some testing like blood work +/- xrays. If he won't take the clavamox in food you need to open his mouth and place the pill as far back on the base of the tongue. Close his mouth and direct it upwards while rubbing his throat to make him swallow it. Follow up with your veterinarian.
If you have additional questions I will be glad to answer them.