What Causes Mild Gas Pain To Turn Into Severe Stomach Ache?

I ve have what started as a mild gas pain this morning and has become more uncomfortable at this time of day. No belching and pain is all over the stomach area was kind of a lower pain and now feels higher in the stomach. I m laying down with a heating pad by it does not seem to be helping. Sometimes the pain gets sharper then subsides then repeats. Thank you...