**Core Concept**
The patient's symptoms are suggestive of a condition that occurs in late pregnancy, characterized by rectal pain and bright red bleeding during defecation. This condition is related to the increased pressure on the pelvic floor and rectal veins.

**Why the Correct Answer is Right**
The most likely cause of these findings is hemorrhoids. Hemorrhoids occur when the veins in the rectum or anus become swollen due to increased pressure from the growing uterus. This increased pressure causes the veins to become distended, leading to pain and bleeding during defecation. After giving birth, the pressure on the pelvic floor is relieved, and the symptoms resolve.

**Why Each Wrong Option is Incorrect**
**Option A:** Anal fissure is a tear in the lining of the anus, which can cause pain and bleeding during defecation. However, it typically presents with a more severe pain and a smaller amount of bleeding. The patient's symptoms are more consistent with hemorrhoids.

**Option B:** Rectal prolapse is a condition where the rectum loses its normal attachments inside the body, allowing it to protrude out through the anus. This condition is often associated with chronic constipation, diarrhea, or straining during bowel movements, which is not the case in this patient.

**Option C:** Rectal cancer is a type of cancer that occurs in the rectum. It typically presents with a change in bowel habits, such as constipation or diarrhea, and may be accompanied by rectal bleeding. However, the patient's symptoms are more consistent with a benign condition like hemorrhoids.

**Option D:** Proctitis is inflammation of the rectum, which can cause bleeding and pain during defecation. However, it is often associated with symptoms such as diarrhea, urgency, and a feeling of incomplete bowel movements, which are not present in this patient.

**Clinical Pearl / High-Yield Fact**
Remember that hemorrhoids are a common condition in pregnancy, and symptoms often resolve after delivery. However, if symptoms persist or worsen, further evaluation is necessary to rule out other conditions.

**Correct Answer:** C. Hemorrhoids