Do not underestimate how black stool points to possible internal bleeding of your digestive system, nor your symptoms of losing weight and having no appetite. This points to the start of a severe health issue that would be more likely benign than malignant. Besides, it's best to go through the colon and intestine diagnostics first as well as some other medical tests.

In some cases, stomach pain can be due to indigestion, inflammation of the stomach, or even a bug in your stomach. Skipping spicy or fat-heavy meals may assist you in this regard. Drinking ginger tea might also relieve you. Furthermore, the liquid intake should be very high.

You mentioned numerous problems that have tortured you in the last 2-3 months - like nausea, fullness after a meal, and heartburn. That can be a sign of anxiety. However, you say that they tend to become aggravated during high-pressure situations such as exams that may lead to that. Anxieties can lead to digestion problems and anticorrelated symptoms. Do some techniques like deep breathing or walking to reduce the stress level. Smaller and more frequent meals can also be of help to avoid your pain. 

Seek medical attention asap for proper evaluation and treatment. There are medications and treatments available for Hepatitis B that can help manage the virus and reduce the risk of long-term liver damage. Ensure to take steps to prevent the spread of the virus to others.

The flu virus can impact digestion, causing nausea and loose­ stools. Along with fever and coughing fits. To recove­r, rest up, stay hydrated, kee­p foods light. But if symptoms worsen alarmingly, reach out to your doctor promptly. They'll advise­ next steps for fee­ling better soon.