Stomach is hard and pain at top of stomach. Feel nauseaus. Had it for 3 days. Indigestion and antacid tablets providing no relief. What could this be?

Stomach. Hard to tell but if its been going on for three days and there is pain and hardness of the stomach you should go to the emergency room.
Abdominal pain. Abdominal pain has many causes and can be difficult to diagnose. Abdominal pain generally requires a visit to a physician for a detailed history and physical to determine the cause.