**Core Concept**
The patient presents with symptoms of rectal bleeding and abdominal pain, which could be indicative of a gastrointestinal issue such as hemorrhoids, diverticulitis, or even more serious conditions like colon cancer. A thorough evaluation is necessary to determine the underlying cause of the bleeding.

**Why the Correct Answer is Right**
The patient's rectal bleeding and abdominal pain, in combination with a normal external and perirectal examination, suggest a possible source of bleeding in the upper gastrointestinal tract or small intestine. The next step would be to perform an endoscopy or colonoscopy to visualize the inside of the rectum, colon, and small intestine, and to identify the source of bleeding.

**Why Each Wrong Option is Incorrect**
* **Option A:** Ordering an X-ray of the abdomen may not be the most appropriate next step, as it may not provide sufficient information about the source of bleeding.
* **Option B:** Prescribing a laxative or stool softener may not address the underlying cause of the bleeding and could potentially worsen the condition.
* **Option C:** Performing a barium enema may not be the best initial step, as it is more of a diagnostic tool for structural abnormalities and may not provide information about the source of bleeding.

**Clinical Pearl / High-Yield Fact**
In cases of rectal bleeding, it is essential to rule out more serious conditions like colon cancer, which can be asymptomatic in early stages. A colonoscopy is a crucial diagnostic tool for evaluating the colon and rectum for polyps, cancer, and other abnormalities.

**Correct Answer: C.**