If you go to this website
Canine Reproduction Video and Book on Breeding and Whelping dogs by Debbie Jensen for dog breeders and Whelping Supplies needed to deliver puppies. scroll down and read every link on the left, you will find tons of informative and important information from the heat cycle, breeding, whelping, and raising a litter of pups. There is even a chart (the Java Due Date) that can estimate your females due date with a week by week chart of things to expect and do.
Also, google "yorkie whelping" and lots of information will come up. Read, read, read, for the next 8-9 weeks to prepare for your possible upcoming litter. That is my most important suggestion for you.
Good Luck.