Hepatocellular Carcinoma (HCC) progression or metastasis: Given the patient's known history of HCC and recent increase in abdominal pain, the most likely diagnosis is progression or metastasis of the existing liver cancer, which could be causing the pain due to tumor growth or invasion into surrounding structures.

Cholecystitis or gallbladder dysfunction: The patient had a cholecystectomy, but issues related to the gallbladder or its removal (e.g., bile duct injury, retained gallstones) could cause right upper abdominal pain.
Peptic Ulcer Disease (PUD): Epigastric pain is a common symptom of PUD, which could be exacerbated or caused by the lack of medication for his condition, potentially including NSAIDs or other irritants.
Liver cirrhosis complications: If the HCC is related to underlying cirrhosis, complications such as portal hypertension, ascites, or hepatic encephalopathy could contribute to abdominal pain.

Budd-Chiari Syndrome: A condition caused by thrombosis of the hepatic veins, which can present with abdominal pain and is particularly relevant in patients with HCC due to the potential for tumor invasion into the hepatic veins.
Spontaneous Bacterial Peritonitis (SBP): A serious infection of the ascitic fluid that can occur in patients with cirrhosis and ascites, presenting with abdominal pain and tenderness.
Hepatic Artery Thrombosis: If the patient has undergone any interventions for his HCC (e.g., transarterial chemoembolization), hepatic artery thrombosis is a potential complication that could cause abdominal pain.

Primary Biliary Cholangitis (PBC) or Primary Sclerosing Cholangitis (PSC): Autoimmune diseases of the liver and bile ducts, respectively, which could cause chronic abdominal pain but are less likely given the patient's presentation and known HCC.
Intra-abdominal metastasis from another primary cancer: Although the patient has a known primary cancer (HCC), it's rare but possible for another primary cancer to metastasize to the abdomen and cause pain.