My GSD had this also, allergy to food and seasonal ones outside...it takes time to build an allergy to food sometimes..it builds up, then all sudden it is getting worse which sounds like it for you..also when she has had an injury to her food, going thru some sticks one stuck her in the foot pad, she bit and licked and caused an infection, took her to doc as soon as I could, and antibiotics and creams and an "bite-not"collar
http://www.bitenot.com/ on her cleared it up. Check and see if you have any wheat, soy or corn in your food, also in any treats you give your dog. Allergy meds could help alleviate the worst of it, but if it is a allergy to food that has to be dealt with. Also check make sure it's not an injury/or old age of some kind like mentioned before.