I have a friend and when I met her it was because her Dexter was throwing up in the mornings and having a hard time sleeping......in talking with her about his diet I found out she was over feeding him at night and giving him kibbles only at night.
I told her to feed him less and to give him can food, he was having a hard time degusting his food during the night and not getting any good sleep.
Some Yorkies have sensitive tummy's, my Duncan is this way if I give him too much Kibbles at any giving time it will up set his tummy