Strange skin problem on older cat.

My 10 year old female cat has suddenly started to bite and chew an area around her tail. The strange thing is that when you touch her there now, she turns her head to the side and starts licking her lips excessively as if a nerve ending was being triggered. She is an indoor only cat and I see no signs of anything on her skin. Any ideas?
Thanks!

has she been tested for worms??

Is she on a flea preventative like Advantage, Frontline, or Revolution? Many cats are allergic to fleas, and a single flea bite can cause a rash and irritation. Even indoor cats can get fleas--they often ride in on our clothing.