Why wont my maltese/yorkie mix stop licking her paws?

My 2yr old maltese/yorkie mix wont stop licking her paws or scratching her face....She is white and champagne and her paws have turned brown from all the licking...I plan on taking her to the vet on monday but just wanted some opinions before then..She also scratches her little face and then licks her paws immediately after...Does anyone know what this could be...Could it be that shes allergic to something?