Everyday stomach aches from indigestion, wind, mild infection or period cramps usually pass within a day or two with rest, fluids and simple measures. See a doctor in the next few days if pain is persistent, recurring, getting worse, or comes with ongoing changes such as altered bowel habit, persistent bloating, heartburn that will not settle, or unexplained weight loss.
Seek urgent care or call your local emergency number if you have sudden severe abdominal pain, a hard or very tender belly, pain with a high fever, repeated vomiting (especially with blood), black or bloody stools, inability to pass stool or wind, pain spreading to the chest, shoulder or back, fainting, or signs of shock such as a racing heart and clammy skin.
Pregnant people with significant abdominal pain, and anyone with severe pain in the lower right abdomen (possible appendicitis), should be seen urgently. When in doubt about severe or unusual pain, it is safer to get checked.