You are likely experiencing acute gastroenteritis. Your immediate priority is preventing dehydration. Please start sipping Oral Rehydration Salts (ORS) or electrolyte solutions slowly. Avoid solid foods for a few hours, then eat a bland diet (rice, toast). You can take a probiotic, but avoid self-prescribing antibiotics or anti-diarrheal medications (like loperamide) without a doctor's evaluation, as they can sometimes worsen the infection. Because you have a combination of severe pain, vomiting, and diarrhea, I highly recommend consulting a healthcare professional for prescription medications like antiemetics. Seek immediate emergency care if you have high fever, blood in your stool, or cannot keep any fluids down.