Itchy mouth in a dog.

For quite sometime now she has been experiencing something that is irritating her around her mouth. I can't rub it enough to satisfy the itch. I cover my hands with my sleeves and rub vigoriously back and forth on the outsides of her mouth. She tries rubbing it on the carpet and with her paws. She will seldom scratch it with her foot. She is on a senior's grain free food. She does seem to have developed allergies to certain foods as she has aged..eggs, beef, and grains (so I keep her away from those as much as possible). She very recently has started expereincing "enviromental" allergies for which I have her on bendryl. Its almost like its a 'yeast infection' around her mouth (at least thats what I can equate it too)....is there such a thing? There is no inflamation. Dakota did have her spleen removed last year as the result of a massive growth on it. But some of the irritation existed before that...it just seems to be getting worse as time goes on...and I feel so bad for her. She is 13.5 yrs old, active and healthy with a great appetite! Thank you for your time. :-)