a 28-year-old woman presents to her primary care provider complaining of abdominal bloating, cramping and diarrhea most days of the week for the last four months. the diarrhea commonly occurs in the morning or following meals. episodes occur four or five times per day and are of moderate volume. she denies fever, nausea, vomiting, periods of constipation, or change in appetite. the diarrhea does not wake her from her sleep and she reports no blood or pus in her stool. she states the periods of diarrhea will last several months and then seem to resolve without explanation. in between diarrhea episodes, she has normal formed bowel movements once per day. a review of her symptom diary reveals no food associations. she denies any recent travel. what is the most likely diagnosis?