It sounds to me that your pup lily had a liver problem. One of my guys that I had a few years ago had it. Unfortunately he passed within 2 weeks. He got very lethargic and seemed very disinterested in food, water, and our other pup. It is very hard to come to terms with because we get so attached so easily. But it is a common problem in yorkies, especially young pups. I am by no means an expert but again, it sounds like your pup had a liver issue.
My pups are just about 7 weeks and are very inquistive and quirky. However, not one pup is exactly alike. They should show interest in food, water, and their littermates as this is a critical period of weaning and socialization. But some pups are naturally shy, which is fine. The red flags are much like you described: lethargic, little/no interest. I say when you get another one, you need to take the pup to the vet to get him/her checked out immediately just to make sure that your pup is indeed healthy.
that's all that I would suggest to you
good luck. Hopefully you will get some more input than just mine.