I am sorry to hear you are worried about Buddy. My name is Rebecca. I am a veterinarian and will do my best to help.
I am worried about him, too. Dogs tend to be secretive about not feeling good, and if they get sick sometimes the only way they let us know that something is wrong is to stop eating. If you look at his gums, are they pink in color? Can you take his temperature at home?
If he were my own dog, I would be checking his gums, taking his temperature, and also listening to his heart and lungs with a stethoscope, feeling his pulse, palpating his internal organs and lymph nodes, etc. He is telling us that something is wrong, and a good physical exam would be the best place to start to try to find out what is the problem.
Since it is a holiday weekend, I would try to get him checked out as soon as you can. Until then, try to keep him hydrated by offering broth or Pedialyte as well as water. If he has not eaten but once in 3 days, he may be dehydrated, which can make whatever is wrong with him even worse.
Let me know how he is doing and what other questions I can answer. Was this helpful?