He has been sick for two days, took him to vet who could not diagnose problem. Gave him antibiotics, pepsid and cerenia for vomiting. He was dehiderated and has lost weight. The vet was not very hopeful. He is a 10 yr old dachshund. He seems to be alert, in no apparent pain, he asks to go out side when needed, and responds to talk at him. He sleeps constantly and will not even look at food or water. How do I get him to eat or drink. He had blood tests that showed no apparent problems, is not running a fever. How long can this go on before I must consider letting him go?