You know usually when a pup has no appetite he needs to be on panacur in case it is giardia also with the coccidia. The giardia is the one that causes loss of appetite.
Sometimes they miss the giardia when they test for it.
I would see if you could get him on a round of Panacur, I think its five days for Giardia. Also are you giving Nutri Cal it has extra vitamins in it the pup needs since he was not eating very well.
First Yorkie I bought had that.
I lost the pup too, he was also only 6 weeks.
That was years ago but still weighs heavy on my heart.
Best of luck with your pup
Deana
Prestigeous