This is serious. The starting and character of the pain is suggestive of Peritonitis. The probable causes are as follows:: Primary peritonitis Perforation of the gastric ulcer Perforation of the small intestine because of Typhoid ot Tuberculosis. Perforated appendicitis. *If the patient is female- Torsion of the Ovarian Cyst, Rupture of the ovarian follicle, Tubal Pregnancy, TO Mass. You need :: X-ray of the abdomen in the standing position for gas under diaphragm Ultrasonography Routine tests of blood, urine, sugar as as per past history. You Need: Admission in the Hospital Intravenous fluids to replenish the third space loss, electrolyte balance, antibiotics and supportive treatment and consent for Surgery if required.