maybe this will help??? --- my Carly (when she was about that same age) starting peeing (a little) frequently, couldn't seem to hold it...I suspected a urinary tract infection (??) something -- and called the vet and he gave her amoxicillan (sp?) and she got better. So it might be something simple, but I'd definitely take a trip to the vet if it doesn't get better in a day or two.
Kendra