I just had my first episode with this and emailed the internal medicine specialist and she said it is rare but in a small percentage of female spayed yorkies incontinence can be the culprit
I looked up incontinence as my yorkie just peed herself and while sleeping and it says it begins in ages 3-5 so this could be it if not a uti and there is a pill for it and it is an easy fix she said. Is your dog on steroids or anything? Here is what i would do - do blood work to rule out diabetes since someone here just mentioned it but our yorkie just had blood work done 8/4 and all was perfect, have culture and urinalysis as this is what internal medicine specialist said to have done and i like free catch rather than needle to bladder but ims said do needle in bladder as more sterile catch and if neither of these things you may have to do the incontinent pills as my gut is that is what your dog has -- now with mine today she peed 3 times in 2 hrs not drinking any water at a yorkie meet up and a few other owners said not normal probably uti so going to do culture and urinalysis to see as she has a staph infection and she is on temarilp which makes them produce more urine than a normal dog so leaning toward uti with her.