A 19 year-old female presents with intermittent episodes of loose stools over the past 6 to 8 months. She admits to crampy abdominal pain and bloating that seems to be more associated with her stress level than with food intake. She denies fever, melena, or nocturnal symptoms. Examination reveals normoactive bowel sounds and mild lower abdominal tenderness on palpation without rebound tenderness or organomegaly. Which of the following is the treatment of choice in this patient? A. Cimetidine (Tagamet) B. Metronidazole (Flagyl) C. Metoclopramide (Reglan) D. Dicyclomine (Bentyl)