**Core Concept**
The case presents with symptoms of chronic abdominal pain, postprandial, accompanied by episodes of passing blood in stools, fever, and weight loss. This clinical presentation is suggestive of a gastrointestinal disorder that requires a differential diagnosis considering various causes of chronic abdominal pain and gastrointestinal bleeding.

**Why the Correct Answer is Right**
The likely diagnosis is **Inflammatory Bowel Disease (IBD)**, specifically **Ulcerative Colitis (UC)**. The patient's symptoms of chronic abdominal pain, postprandial, fever, weight loss, and episodes of passing blood in stools are characteristic of IBD. Ulcerative colitis is an inflammatory condition that affects the colon, leading to inflammation and ulceration of the colonic mucosa, which may cause bleeding, diarrhea, and abdominal pain.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not mentioned in the question.
* **Option B:** Other causes of gastrointestinal bleeding such as **Peptic Ulcer Disease (PUD)**, **Gastroesophageal Reflux Disease (GERD)**, and **Infectious Colitis** can be ruled out as the patient's symptoms are more chronic in nature and not acute.
* **Option C:** **Celiac Disease** is a chronic autoimmune disorder that causes small intestine damage due to gluten ingestion, but it typically presents with diarrhea, abdominal pain, and weight loss without significant gastrointestinal bleeding.
* **Option D:** **Intussusception** is a condition where a part of the intestine telescopes into another part, causing bowel obstruction and potentially leading to intestinal necrosis, but it typically presents with acute abdominal pain and vomiting in children.

**Clinical Pearl / High-Yield Fact**
Chronic abdominal pain and gastrointestinal bleeding in a young patient should raise suspicion for IBD, and a prompt evaluation with endoscopy and biopsy is crucial for an accurate diagnosis.

**Correct Answer:** D.