Reaction to anesthesia or procedure: Mild fever and fatigue 2 hours post-ERCP stent placement under general anesthesia could most likely be attributed to the body's reaction to the anesthesia or the procedure itself. This is a common and usually transient response.

Cholecystitis or pancreatitis: Although less common, these conditions can occur as complications of ERCP, especially if there was manipulation of the biliary or pancreatic ducts. Symptoms could include fever and fatigue, among others.
Bile duct injury or leak: This is another potential complication of ERCP that could lead to symptoms such as fever and possibly fatigue, depending on the severity of the injury.
Infection at the site of stent placement: Early signs of infection could include mild fever and fatigue, although this might be less common so soon after the procedure.

Sepsis: Although unlikely to present so early and mildly, sepsis is a potentially life-threatening condition that could arise from complications related to the ERCP procedure, such as an infected bile duct. It's crucial to monitor for signs of sepsis, including fever, which could initially be mild.
Perforation of the GI tract: A rare but serious complication of ERCP that requires immediate attention. Early signs might be nonspecific, including fever and fatigue, but the condition can rapidly deteriorate.

Allergic reaction to contrast media: If contrast was used during the ERCP, an allergic reaction could potentially cause symptoms like fever and fatigue, although this is relatively rare and usually more immediate.
Stent migration or occlusion: While not typically presenting with fever and fatigue as primary symptoms, stent migration or occlusion could lead to complications that might include these symptoms, especially if there's associated infection or pancreatitis.