Welcome to YT!
Sounds like your little gal might have some allergies-they can be caused by the change in seasons, detergents or other things in the house, or the food she's eating. My first guess would be the food-many dogs have corn/wheat allergies that can make them itchy.
Check out the different dog foods at
www.dogfoodanalysis.com
Most yorkie owners would recommend a 4-5 star food for their pets. The 6 star foods are for working dogs-they're too much for what yorkies need. As you can see, Pedigree isn't a high quality food.
You might also talk to your vet and see if there is something you should be supplementing with, such as vitamins, nutrical, or other foods.