My DS is potty training this week, it's going really well thus far.
However, when he is on the toilet he often gags - and even retches a bit. This is for a wee - we haven't had a successful poo on the potty as yet!
He has been known to gag when he has done a particularly nasty poo, in his nappy, but I don't know why he is now doing it after a wee!