4-month Nonspecific Crampy Abdominal in Medicine / Internal Medicine — 28yo Man | Gastroenterology | SMLE Q#8193

A 28-year-old man presents to the outpatient clinic with a 4-month history of nonspecific crampy abdominal pain and bowel habit changes. He reports episodes of loose stools alternating with constipation. The symptoms are not related to any specific type of food, and there is no history of food allergy. He denies rectal bleeding, nocturnal diarrhea, fever, or unintended weight loss. His appetite is normal, and his weight has been stable. Vital signs: T: 36.6 °C, BP: 110/70 mmHg, HR: 76/min, RR: 14/min, SpO2: 99% on room air. BMI is 23 kg/m². Physical examination, including abdominal exam, is unremarkable. Which of the following is the most likely diagnosis?