Intestinal Obstruction: The combination of not opening bowels for 3 days, not passing wind, and diffuse abdominal tenderness, along with nausea and vomiting, strongly suggests an intestinal obstruction. The pain and tenderness, especially with the examination being too painful to continue, support this diagnosis.

Acute Appendicitis: Although the pain is on the left side, which is less common for appendicitis, the symptoms of nausea, vomiting, pyrexia, and abdominal tenderness could still align with an atypical presentation of appendicitis, especially if the appendix is retrocecal or in an unusual position.
Diverticulitis: Given the left flank pain and the presence of pyrexia, diverticulitis is a plausible diagnosis, especially if the patient has a history of diverticular disease. The abdominal tenderness and difficulty with bowel movements could also fit this diagnosis.
Kidney Stone or Pyelonephritis: The left flank pain and pyrexia could indicate a renal issue such as a kidney stone or pyelonephritis. However, the absence of specific urinary symptoms (like dysuria or hematuria) and the diffuse abdominal tenderness make these less likely but still possible.

Perforated Viscus: This is a surgical emergency that could present with severe abdominal pain, tenderness, and guarding. The fact that the physical examination had to be stopped due to pain raises concern for a perforation.
Mesenteric Ischemia: Although less common, this condition can present with severe abdominal pain out of proportion to the physical examination findings, along with signs of bowel obstruction. It's a high-mortality condition if not promptly diagnosed and treated.
Ectopic Pregnancy: In females of childbearing age, an ectopic pregnancy could present with abdominal pain, nausea, vomiting, and could potentially lead to severe consequences if missed.

Inflammatory Bowel Disease (IBD) Flare: While IBD (like Crohn's disease or ulcerative colitis) can cause significant abdominal symptoms, the acute onset of symptoms described, especially the inability to pass wind and the severe pain, makes this a less likely but possible diagnosis.
Ovarian Torsion: Similar to ectopic pregnancy, ovarian torsion is a rare but serious condition that could present with acute abdominal pain and should be considered in the differential diagnosis of females, especially if there's a history of ovarian cysts.