I had to have the vet express my dogs anal glands once. He was draging his bottom on the carpet a lot. He was sick with diareah and not eating at the time though so I definately suggest you see a vet if this is happening. It is not common but can happen to some yorkies. I don't know if it is from illness or it just happens, but it only happened bad when he was sick. Once in a great while he will still drag his bum, but hasn't indicated any discomfort or do it often enough for me to be concerned. Note he showed his discomfort when he was sick. It's funny and very gross when he does it. The look on his face is hillarious! Must be just itchy...
Yorkies are so cute even when they are doing the worst things, arent they?