Nephrolithiasis (Kidney Stones): This condition is a common cause of flank pain, often accompanied by nausea and vomiting. The pain can be severe and may radiate to the groin. The presence of nausea suggests an obstructive cause, which is consistent with a kidney stone.

Pyelonephritis: An infection of the kidney, which can cause flank pain, nausea, and vomiting. It is more common in women and often associated with symptoms of urinary tract infection.
Appendicitis (with atypical presentation): Although appendicitis typically presents with right lower quadrant pain, some cases may have an atypical presentation with flank pain, especially if the appendix is retrocecal.
Gastroenteritis: Inflammation of the stomach and intestines, which can cause nausea, vomiting, and abdominal pain that may radiate to the flanks.

Ruptured Abdominal Aortic Aneurysm: A life-threatening condition that requires immediate attention. Although it typically presents with severe abdominal pain, it can sometimes cause flank pain and nausea.
Ectopic Pregnancy: A pregnancy that develops outside the uterus, which can cause severe abdominal or flank pain, nausea, and vomiting. It is a medical emergency.
Pulmonary Embolism: A blood clot in the lungs, which can cause sudden onset of chest pain, shortness of breath, and may also cause flank pain if the clot is large enough to cause referred pain.

Renal Infarction: A blockage of the blood supply to the kidney, which can cause severe flank pain and nausea. It is less common than other causes of flank pain but should be considered in patients with risk factors for thromboembolism.
Retroperitoneal Hemorrhage: Bleeding into the space behind the peritoneum, which can cause flank pain, nausea, and vomiting. It is often associated with trauma or anticoagulation therapy.