Recently started trying to potty train DS (2.5). He completely understands what it's for, is aware of need to go, etc, and has on a few occasions in the past actually taken himself to the potty and done a poo. All of this was received with lots of praise and congratulations (and chocolate buttons) and he was proud of himself etc. He's never ever been told off for making a mess on the floor or told it was "dirty" or anything like that.
BUT... although he previously willingly had a few goes on the potty, he now refuses to go on it, and if he has his nappy off and needs to go he gets very upset and begs for a nappy on. He will hold it all in for hours until I finally put a nappy on him and then will immediately poo/wee. I've tried asking him what it is about the potty (or toilet) that he doesn't like but he can't express what the problem is. I get the impression he's a bit scared of the feeling of exposure from doing a poo/wee with a bare bottom and prefers to feel it all comfy in his nappy (?!).
Any ideas? I'm afraid I will just make it worse if I keep going with our current methods. I've thought about giving up completely and coming back to it in a month or so but that just seems to be postponing the problem rather than dealing with it.