Viral Hepatitis: The patient's symptoms of fever, vomiting, and significantly elevated liver enzymes (AST 149, ALT 176, alk phos 283) are consistent with viral hepatitis, which is a common cause of acute liver injury in young adults. The mild tenderness could be indicative of hepatitis-related liver inflammation.

Alcoholic Hepatitis: Although less likely in an 18-year-old, alcoholic hepatitis could present with similar laboratory findings and should be considered, especially if there's a history of alcohol consumption.
Drug-induced Liver Injury (DILI): Various medications and substances can cause liver enzyme elevations. Given the patient's age, over-the-counter medications, supplements, or recreational drugs could be potential culprits.
Mononucleosis: Caused by Epstein-Barr virus, it can lead to liver enzyme elevations, fever, and vomiting, although it more commonly presents with lymphadenopathy and sore throat.

Acetaminophen Overdose: A leading cause of acute liver failure, acetaminophen overdose must be considered, especially with elevated liver enzymes. Early recognition is crucial for effective treatment with N-acetylcysteine.
Wilson's Disease: Although rare, Wilson's disease can present acutely with liver dysfunction and should be considered to avoid missing this potentially treatable condition.

Autoimmune Hepatitis: An autoimmune condition that can cause liver inflammation and elevated liver enzymes. It's less common and typically presents with more chronic symptoms but can have an acute presentation.
Budd-Chiari Syndrome: A rare condition caused by hepatic vein thrombosis, leading to liver dysfunction. It's an important consideration due to its potential for severe outcomes if not promptly treated.
Ischemic Hepatitis (Shock Liver): Caused by decreased blood flow to the liver, it can result in significantly elevated liver enzymes. This condition would be unusual without a clear history of shock or severe hypoperfusion.