A 45-year-old male presents to the outpatient clinic with a 6-month history of intermittent lower abdominal discomfort, often described as cramping, which he notes is frequently relieved by defecation. His bowel habits have been inconsistent, characterized by periods of increased stool frequency and urgency, sometimes with loose stools, alternating with episodes of mild constipation. A concerning symptom he reports is nocturnal awakenings due to severe abdominal cramps followed by urgent diarrhea. He also mentions a recent onset of unexplained fatigue and a general sense of malaise. On physical examination, his abdomen is diffusely tender upon palpation in the lower quadrants, but without rebound tenderness or guarding. Rectal examination reveals normal sphincter tone and brown, guaiac-negative stool in the vault. Given his presentation and laboratory findings, what is the most probable underlying condition and the immediate diagnostic and management approach?

A 28-year-old man presents to the gastroenterology outpatient clinic complaining of recurrent abdominal pain and altered bowel habits spanning the past seven months. He describes the pain as crampy, often located in the lower abdomen, which frequently improves after a bowel movement. His bowel movements are characterized by periods of urgent, loose stools, typically 3-4 times a day, alternating occasionally with brief episodes of constipation, but predominantly diarrheal. He reports no weight loss, fever, or rectal bleeding. He admits to significant work-related stress, which he believes exacerbates his symptoms. On physical examination, he is afebrile with stable vital signs. Abdominal palpation reveals mild diffuse tenderness without rebound or guarding. No masses or organomegaly are noted. Based on these findings, what is the most appropriate diagnosis and the initial pharmacological intervention to consider for his predominant symptom?

A 52-year-old male presents to a general medical clinic with a 7-month history of intermittent lower abdominal discomfort. He describes the pain as cramping, frequently relieved by defecation, and associated with fluctuating bowel habits, ranging from episodes of loose stools occurring several times a day to periods of infrequent bowel movements lasting up to five days. He has recently tried various over-the-counter remedies and dietary changes, including a strict lactose-free diet, with minimal sustained relief. He reports no significant weight loss, fever, or overt gastrointestinal bleeding. His past medical history includes essential hypertension managed with lisinopril and a mild anxiety disorder for which he takes no current medication. His mother was diagnosed with colorectal cancer at age 62. On physical examination, there is mild diffuse tenderness upon deep palpation of the lower quadrants, but no guarding, rebound, or organomegaly. Rectal examination reveals no masses, and a fecal occult blood test is negative. Laboratory results show: Hemoglobin 145 g/L, White Blood Cell Count 7.2 x 10^9/L, Erythrocyte Sedimentation Rate 10 mm/hr, and C-reactive protein 2.5 mg/L. Given his presentation and the need to rule out more serious pathology, what is the most appropriate initial diagnostic procedure, and what non-pharmacologic intervention should be considered if a functional bowel disorder is confirmed?