Dr. Stephanie Arnold's patient was so uncomfortable she asked for a same day appointment. The suspect: a vaginal yeast infection. But there was some mystery, too. The patient had used a one-day, over-the-counter treatment for the problem. Why was she still in pain a week later? Arnold examined her patient, took a swab to look at under the microscope and found no evidence of yeast or bacteria. “I think it’s chemical irritation,” Arnold explained to her patient back in the exam room.