Stress over pooing

[IWroteToTheZoo]

We started potty training 2.5yr DS about 3 weeks ago, and so far, weeing in the potty has happened pretty much without a hitch - asks for potty, pleased as punch when he does one and no accidents to speak of.

When we started out, he had a couple of poo accidents that seemed to really scare him - inconsolable crying. We reassured him, and since then have rewarded him with stickers etc. for the couple of times small amounts have actually got into the potty (more from us realising and putting him on it than him doing it himself.)

He now seems not to be stressed about pooing any more - in fact, after much talk of special stickers and smarties he'll get for doing it in potty, he's desperate to do it, and asks many, many times a day to "do a poo on the potty", but then ... nothing. It's almost like he's constipated, he hasn't pooed for a couple of days, despite saying he wants to. Not pooing is stressing him out now, and even if I put a nappy on him, he insists on taking it off and trying the potty - but nothing! I would be thinking that maybe he's just not ready, and giving up, but he's so good with weeing, seems so keen, and now doesn't want to wear a nappy at all.

Could he have made himself constipated through the early stress over pooing? Should we give up for now?

Any advice would be appreciated - think I'm more stressed about it than he is by this point!