Poor baby!
There are glands at the base of the tail that can be affected by allergies. Do you notice her licking/chewing her front legs/paws or are the inside of her ears red? These are also signs of allergies. Probably food, as I doubt there's too much in the air in Indiana at this time of year to upset her.
Does she seem to be straining to go potty? Could she be just a little constipated? Do you notice her scooting her butt on the floor? A little canned pumpkin can help to regulate her. Real pumpkin, not the pumpkin pie filling.
You can always call your vet to see if they have any ideas/suggestions.