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.