If the pain is actually in your stomach than it could be related to an Ulcer, GERD, Hiatal Hernia or Gastritis, again just to name a few. The abdominal cavity contains many of our vital organs
and without a good clinical exam
and possibly some additional testing it can be difficult to diagnosis.
In my opinion if your pain is sudden and acute you should seek an immediate medical evaluation. If it is more chronic than it is still time to make an appointment with your PCP.