Baby Gas?

girlyjo

DS basically screams (face slowly turning purple) and flails around. Yes, he pulls his legs up, but he seems to do that often anyway, even when he's not fussing. Sometimes there are no cues, he just suddenly breaks into a cry that reaches a scream really quickly. He quiets down for a little bit when we sit him upright but he doesn't pass gas or burp or anything - just calms down for a few minutes.

So my questions are: How do you know if it's gas that makes your child fuss? When do you give gas drops? How long do they take to work?