Gastrointestinal Motility Disorder: Given the history of total colectomy, which is often performed for conditions like ulcerative colitis or familial adenomatous polyposis, and the symptoms of abdominal pain and frequent vomiting, a gastrointestinal motility disorder such as gastroparesis is highly plausible. The removal of the colon can sometimes lead to or exacerbate issues with the movement of food through the digestive system.

Small Intestine Bacterial Overgrowth (SIBO): This condition can occur after significant alterations to the gastrointestinal tract, such as a total colectomy. SIBO leads to bloating, abdominal pain, and vomiting due to the abnormal growth of bacteria in the small intestine.
Short Bowel Syndrome: Although less common, if a significant portion of the small intestine was removed or is not functioning properly during or after the total colectomy, this could lead to malabsorption, abdominal pain, and vomiting.
Adhesions or Bowel Obstruction: Post-surgical adhesions can cause bowel obstruction, leading to severe abdominal pain and vomiting. This is a common complication after abdominal surgeries.

Intestinal Ischemia: This is a potentially life-threatening condition where there is insufficient blood flow to the intestines. It could be a complication of the surgery or unrelated but needs to be considered due to its high mortality rate if not promptly treated.
Medication-Induced Side Effects: Certain medications, especially those used to manage conditions post-colectomy or for pain, can cause significant gastrointestinal side effects, including vomiting.

Rapid Gastric Emptying (Dumping Syndrome): This condition can occur after certain types of gastrointestinal surgery, leading to symptoms like vomiting, abdominal cramps, and diarrhea after eating.
Neuroendocrine Tumors: Although rare, these tumors can cause a variety of gastrointestinal symptoms, including abdominal pain and vomiting, and might be considered in the differential diagnosis if other causes are ruled out.