Ds (just turned 3) started potty training on Saturday and as expected, it's a mess 
What's worried me is him holding onto his his poos. It's quite normal for him to poo 3 times a day but since Saturday, we've had 1 malteser size in potty a few hours into it, a big poo in Sunday mornings pull up and the HUGEST poo I've ever seen, today, after a couple of hours of complaining he had tummy ache!!!!
He held it in as long as he could then (by choice) did it in his pants - what a mess!!! After chatting for a while, I finally found out why he wouldn't go to the potty (as this was not an accident!). He said his reason was he was worried about getting poo all over the carpet - I have told him not to worry about that as it would just go in the potty but he obviously thinks his bum hangs outside the potty!!! 
Is this normal? Any tips?