Small Bowel Obstruction: Given the patient's history of a stricture, worsening abdominal pain, nausea, vomiting, and decreased bowel movements, small bowel obstruction is a highly plausible diagnosis. The stricture could be causing a mechanical obstruction, leading to the patient's symptoms.

Gastroenteritis: The patient's symptoms of nausea, vomiting, and abdominal pain could be indicative of gastroenteritis, especially if the patient has been experiencing decreased bowel movements and has not been able to eat or drink much.
Inflammatory Bowel Disease (IBD) Flare: The patient's history of a stricture and current symptoms could suggest an IBD flare, particularly if the stricture is related to Crohn's disease or ulcerative colitis.
Constipation: Although less likely given the acute worsening of symptoms, constipation could be a contributing factor, especially if the patient has not been having normal bowel movements.

Appendicitis: Although the pain is in the upper quadrants, appendicitis can sometimes present with atypical pain locations, and missing this diagnosis could be catastrophic.
Mesenteric Ischemia: This is a life-threatening condition that could present with abdominal pain, nausea, and vomiting, especially in older adults.
Perforated Viscus: A perforation in the gastrointestinal tract could lead to severe abdominal pain, nausea, and vomiting, and is a medical emergency.

Intussusception: A rare condition where a part of the intestine telescopes into another, causing obstruction and potentially severe abdominal pain.
Malrotation with Volvulus: A rare condition where the intestine twists around its mesentery, causing obstruction and potentially severe abdominal pain.
Abdominal Malignancy: Although less likely, abdominal malignancies such as lymphoma or carcinoid tumors could present with abdominal pain, nausea, and vomiting, and should be considered in the differential diagnosis.