A positive HBsAg test means you have Hepatitis B. Please do not panic; in most adults, sudden infections clear up completely on their own. If it is a long-term infection, it is highly manageable with modern treatment, though not always fully curable. Your stomach pain needs evaluation. Before taking any antiviral medicines, like tenofovir or entecavir, you must consult a gastroenterologist. They will run further tests (like liver function and viral load) to decide if medication is actually needed. Please avoid self-medication, limit alcohol, and consult a doctor soon.