Ghilly and Karla have given you good advice. Don't leave this or your little guy may not make it through to Monday. Get him to a vet as quickly as you can. He absolutely needs both hydration and nutrition to give him energy and to prevent his organs from closing down, which your vet can undertake as an emergency. Then, after that, it's time to diagnose what's wrong, and taking a blood sample will probably facilitate that. Let us know what the vet says ... and fingers crossed that the underlying cause is not something life threatening at this stage. Tony
Welcome to the forum......If your guy has indeed gone this long without nutrition, Hypoglycemia is probably occurring....Three days is as long as a Tiny dog can go without food & water, Period....IMO, you have an Emergency on your hands, due to his size......
Hypoglycemia & dehydration can be Fatal in a short period of time........Especially in Tiny Breeds....I would not wait until Monday to seek treatment.....You need to find somewhere tonight to have him treated...He needs to be on IV Fluids to sustain his body, until the Vet can determine what is wrong.....Please, do not wait any longer or he is not going to make it.......
I do wish you luck & I hope he is OK......Let us know....... Karla
Unfortunately, there is nothing that we here on the forum can do to help other than to suggest that you make an appointment for him at the vet ASAP. There's no telling what it might be at his age, and when they are seniors like that, it can be anything from a bad tooth that's hurting him that is curable with an antibiotic to something very serious, like liver failure. The only one who can tell is his vet. Please keep us updated on how he is and what the vet says.
Ghilly