every kid is different, though often they squirm or grunt when they have to poo. do you notice that the poo happens at a certain time of day? usually mornings, or evenings? after he's been fed? my DS was so regular with his pees and poops, i could practically set the clock to it once i figured out his patterns.
you might want to keep a paper and pen handy for a week or so, jot down times you feed, and when baby pees or poos and see if you can start noticing some patterns. i found that incredibly helpful when i started out.
yoga teacher and mama to DD River 5/03 DS Solomon 7/05 and DD Elowyn 5/08