lol....
I do not think what you are describing is gas in your stomach.
If you had gas in your stomach, you would burp.
I find it amusing when people have physical ailments and they come up with stuff that doesen't really even make sense when you think about it for more than 0.05 seconds
Anyway, what you are probably describing is your stomach cramping because it is empty(and emptying itself). To most people, this feeling is very uncomfortable and demands immediate attention(eating will cure it nearly instantly).
I describe it as feeling like my stomach is imploding, lol..