stupid gas question

Chunstad

You'd think that I'd know this, but how do I absolutely know that baby's distress is gas?  Obviously, I'll go through and make sure he's not hungry/dirty pants/uncomfortable in his position.  The reason I'm asking is that I finally broke down and bought some gas drops-I don't want to go using them willy nilly, I want to really make sure that I am using them when I should be.  Is this unrealistic?