**Core Concept**
The infant's symptoms suggest an intestinal obstruction or motility disorder, as evidenced by recurrent episodes of abdominal pain and altered stool passage without vomiting or rectal bleeding. This presentation is consistent with a condition characterized by abnormal intestinal peristalsis and obstruction.

**Why the Correct Answer is Right**
The most likely diagnosis in this scenario is _Intussusception_. Intussusception occurs when a segment of the intestine telescopes into another segment, leading to obstruction and potentially ischemic damage. This condition often presents in infants with abdominal pain, altered stool passage, and may be accompanied by a characteristic "currant jelly" stool due to the presence of blood and mucus. The pathophysiology involves abnormal intestinal motility and the presence of a lead point, such as a Peyer's patch or Meckel's diverticulum.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, but typically, other conditions such as _Hirschsprung's disease_ or _Gastroesophageal reflux disease (GERD)_ might be considered as alternative diagnoses, although they do not typically present with altered stool passage and abdominal pain without vomiting.
* **Option B:** _Appendicitis_ is unlikely, as it typically presents with abdominal pain, vomiting, and fever, and is more common in older children and adults.
* **Option C:** _Inflammatory bowel disease (IBD)_ is unlikely, as it typically presents with chronic diarrhea, abdominal pain, and weight loss, and is more common in older children and adults.
* **Option D:** _Gastroenteritis_ is unlikely, as it typically presents with vomiting, diarrhea, and fever, and is more common in younger children.

**Clinical Pearl / High-Yield Fact**
Intussusception is a medical emergency requiring prompt diagnosis and treatment, as it can lead to bowel ischemia and necrosis if left untreated.

**Correct Answer:** C. Intussusception.