Need help with my 2 1/2 year old.

He seems to understand things very well but then he is so uncontrollably hyper. He can't sit still for more than a few minutes. We have been trying to potty train and that is going out the window. He was doing really good about not pottying in pants and now he will only potty in his pants. I can take him to the bathroom and he will tell me that he doesn't need to potty and then not even 5 minutes later he has pottied in his pants. Am I doing something wrong. I need some advice. Make note that this is the first child I have tried to potty train.