He missed one vaccination and I think that may be the cause.
However, I think it is more so that he may have also ate something he shouldn't have eaten because he was well until a family event this weekend.I'm not exactly sure what he could have eaten as the kids were feeding them stuff here and there but after the event all the dogs, we have two other dogs, loss their appetite but the older dogs are okay now. He has not suffered and trauma and there are signs of vomiting and diarrhea.
It sounds to me like your dog may have come down with pancreatitis from eating the people food. Pancreatitis happens when a dog eats fatty foods and can be a fatal illness if left untreated. Your dog needs medications to help him feel better and even an IV catheter to help ward off dehydration.
More information on pancreatitis is here:
Because it has been going on for several days, I would NOT wait to have him seen by a vet. If there is an emergency vet in your area, I strongly urge you to get him there and have them take a peek at him, get him on some medication to help him feel better and provide supportive care until the threat passes and he's feeling better. I would also cut out any people food that he gets. Once a dog gets pancreatitis, it seems like they're more likely to get it after that.
If there is no emergency vet in your area, then seeing your own vet in the morning is acceptable. They'll get him feeling better soon!
I hope this helps.