Post-operative ileus: This condition is characterized by a temporary halt of the normal contractions of the bowel muscles, which can occur after abdominal surgery. The presence of abdominal pain, vomiting, and reduced bowel sounds (2 per minute) in a post-operative patient makes this a highly plausible diagnosis. The fact that the patient has stable hemodynamics and a non-tender abdomen also supports this diagnosis, as post-operative ileus typically does not cause peritonitis or severe abdominal tenderness.

Constipation: The repeated urge to pass urine could be a sign of urinary retention due to constipation, which is common post-operatively due to pain, immobility, and opioid use. Abdominal pain and vomiting can also be associated with constipation.
Urinary Retention: Directly related to the repeated urge to urinate, this could be due to post-operative pain, especially if the hernia repair involved areas near the urinary system, or due to the effects of anesthesia.
Gastroenteritis: Although less likely in a post-operative setting without a clear source of infection, gastroenteritis could cause abdominal pain, vomiting, and altered bowel habits.

Intestinal Obstruction: A serious complication that could arise post-operatively, especially after hernia repair. Symptoms can include abdominal pain, vomiting, and altered bowel sounds. Early diagnosis is crucial to prevent severe complications.
Perforation: Although the patient's abdomen is non-tender, any sign of peritonitis or free air under the diaphragm on imaging would indicate a perforation, which is a surgical emergency.
Bleeding or Hematoma: Internal bleeding or a hematoma at the surgical site could cause abdominal pain and vomiting. The fact that the patient is hemodynamically stable reduces the likelihood but does not rule it out entirely.

Adhesional Band: Although rare in the immediate post-operative period, adhesional bands causing bowel obstruction can occur. These are bands of fibrous tissue that can form between loops of bowel or between the bowel and the abdominal wall, potentially causing obstruction.
Intra-abdominal Abscess: An abscess could form as a complication of the surgery, especially if there was any contamination during the procedure. However, this would typically present with signs of infection such as fever, tenderness, and possibly a palpable mass, which are not mentioned in the scenario.