My yorkie has about 10 to 12 days left in her pregnancy, and she have not produced any milk yet, is that OK? Or should I take her to the vet again?

Some b*tches will only start producing milk in the last week of pregnancy. I wouldn't worry yet, just call your vet and just let them know what is going on in case you have to make a trip next week. It's better to let them know now so they can pencil you in, especially if your vet is a busy one and you have trouble getting last minute appointments.