I am Dr Shamoon. Stomach pain after prolonged fasting can be due to acidity or gastritis, but unbearable pain should not be assumed to be simple gas. The exact location, vomiting, fever and bowel symptoms help decide the cause.
Next Steps
Take small, light meals and fluids rather than a heavy dinner, but avoid painkillers such as ibuprofen on an empty stomach. Seek urgent care today if pain is severe or persistent, or with repeated vomiting, fever, black stools, faintness or a rigid abdomen. You may book a Practo consultation for review.