What Causes Frequent Urination?

My daughter has been having odd accidents. She seems to have to have to pee quite often but she hasn t been drinking more or anything out of the ordinary. When she goes, she goes as normal, no pain/discomfort, no odor, or anything like that. I have no idea what s causing this. I just too her to the bathroom and just a few minutes later she came to me and said she was wet and had an accident. She s three years old (born 10/18/11). She s been potty trained since she was two. I plan on making her a doctors appointment tomorrow but I m hoping for some kind of answer before then. Thank you.