Obstruction of the ureteral stent: This is the most likely diagnosis given the patient's recent history of PCNL and the presence of a ureteral stent. The symptoms of nausea and weakness, along with the elevated creatinine level, suggest that the stent may be obstructed, leading to acute kidney injury.

Sepsis: The patient's elevated WBC count and symptoms of nausea and weakness could indicate a post-operative infection, which is a common complication after PCNL.
Bleeding or hematoma: Although the patient's hemoglobin is currently at 11, which is not significantly low, the possibility of internal bleeding or a hematoma causing the patient's symptoms and renal impairment cannot be ruled out without further investigation.
Acute kidney injury (AKI) from other causes: Other causes of AKI, such as medication-induced nephrotoxicity, contrast-induced nephropathy (if contrast was used during the procedure), or pre-renal causes like dehydration, should also be considered.

Septic shock: Although the patient's current presentation does not fully align with septic shock, missing this diagnosis could be fatal. Close monitoring and repeated assessments are crucial.
Pulmonary embolism: Post-operative patients are at increased risk for venous thromboembolism, including pulmonary embolism, which can present with non-specific symptoms like weakness and could be masked by other post-operative complications.
Retroperitoneal hemorrhage: A significant and potentially life-threatening complication that requires immediate intervention. The patient's symptoms and lab results do not strongly suggest this, but it cannot be missed.

Tumor lysis syndrome: Although rare in this context, if the patient had an unrecognized renal tumor that was affected during the PCNL, tumor lysis syndrome could occur, leading to acute kidney injury.
Allergic interstitial nephritis: An allergic reaction to medications, including antibiotics that might have been prescribed post-operatively, could cause interstitial nephritis, leading to renal impairment.