Alcoholic Hepatitis: This condition is a likely cause given the patient's history of fatty liver infiltration and sudden weight gain after drinking alcohol. Alcoholic hepatitis can lead to fluid retention and weight gain due to the liver's decreased ability to metabolize and detoxify substances.

Alcohol-Induced Pancreatitis: Pancreatitis can cause abdominal pain, nausea, and vomiting, but it can also lead to weight gain due to fluid accumulation and decreased pancreatic enzyme production affecting digestion and nutrient absorption.
Hepatic Congestive Syndrome: In patients with liver disease, the liver's decreased function can lead to fluid buildup in the body, causing weight gain. This condition can be exacerbated by alcohol consumption.
Nutritional Factors: Alcohol contains calories, and excessive consumption can lead to sudden weight gain, especially if the patient is not adjusting their diet accordingly.

Spontaneous Bacterial Peritonitis (SBP): Although less common, SBP is a serious condition that can occur in patients with liver disease and ascites. It requires prompt diagnosis and treatment to prevent high mortality rates.
Hepatorenal Syndrome: This is a type of kidney dysfunction that occurs in patients with advanced liver disease. It can lead to fluid retention and weight gain and is critical to diagnose early due to its high mortality rate if left untreated.

Budd-Chiari Syndrome: A rare condition caused by thrombosis of the hepatic veins, leading to liver congestion, ascites, and potentially sudden weight gain. It's more common in patients with thrombophilic conditions but should be considered in the differential diagnosis of liver disease and sudden weight gain.
Hepatic Veno-Occlusive Disease: Also known as sinusoidal obstruction syndrome, this is a rare condition that can occur after certain medications or in the setting of hematopoietic stem cell transplantation. It leads to hepatic venule occlusion, causing liver dysfunction and potentially weight gain due to fluid retention.