Toilet training-Is this normal???

I posted about this child before, but I have a 2 year old who is potty training. Over the holidays he became completely trained with his parents, but with me he does not want to use the toilet. We struggled through last week, but now it is even worse. He is holding it..he doesn't want to go in his pull-up, but won't go on the potty or toilet. His mom said he started holding it at home yesterday too...for 5 hours he held it until he finally burst and soaked through his pull-up and pants. Today he is clearly in agony. He is twisted and making sounds like a woman in labour and obviously has to go BAD, but he cries when I put him on the toilet (I tried leaving him there to cry for awhile, but he still holds it!). Finally I asked him if he wants a diaper and he said yes, so I put him in a diaper and told him he can pee or poop in it if he needs to. He was still really uncomfortable and I am not sure if he has peed yet. Is this normal?? What can I do to help this poor kid? I am at a loss!

Is he going on the toilet or a potty at home? Does he sit or stand at home? Maybe make sure its the same otherwise I don't know! Poor little guy

Does he have the communication skills yet to ask him if it HURTS to go potty? If he has a urinary tract infection or something like that, he might be afraid to go.
Either that or (and I hate to say this) it sounds like someone has scared the bejeebers out of this little guy. As in; "if you pee/poop your pants, BAD things will happen!!". A friend of mine used to tell her kids odd things like, "If you have an accident, the dinosaurs will come and eat you." Needless to say, it had a tendency to backfire on her. If this has happened, he may have developed some serious mental issues with toileting. Honestly, I would put him back into diapers and try this again a few months from now.