For immediate relief from acidity and mild stomach pain, you can take an over-the-counter antacid containing magnesium hydroxide or calcium carbonate. Alternatively, an H2 blocker like famotidine, or a proton pump inhibitor like omeprazole (taken 30 minutes before a meal), can reduce acid production effectively. Avoid spicy, oily, or acidic foods, and try to eat smaller, more frequent meals. Stay hydrated and avoid lying down immediately after eating. If your pain is severe, accompanied by fever, vomiting, or dark stools, or if it doesn't improve after a couple of days, please consult a healthcare professional for a proper diagnosis.