potty training issue

Ever since my son has learned how to go to the bathroom (both 1 & 2), he refuses to wear underwear.  He says that he is afraid that he'll pee in his underwear so he insists on a pull up.  I have tried to tell him we don't have any pull ups, etc.  He'll go the whole day without anything on and he will literally spend most of the day on the toilet because he thinks that he has to go to the bathroom.  Of course, nothing comes out most of the time, but he still has this irrational fear that he will go in his underwear.  Mind you, he has NEVER even had an accident in his underwear once he learned how to use the toilet.  Plus, I never made an issue if he DID have an accident, so I don't understand where this fear is coming from.

Also, he was going to preschool, which he LOVED (2 days a week for only two hours).  The problem was that he had to be potty trained.  Well, he wasn't, but I knew he'd never have an accident, so I sent him in underwear and he did great.  As SOON as he went to the bathroom on the toilet, he refused the underwear and had to leave the preschool he loved.  He seems genuinely afraid to wear underwear because he may have an accident (which he won't, but who cares if he does??)

Can anyone give me ANY ideas or comments about this???  I just don't understand what is going on.  It's very frustrating.  My son will turn 3 1/2 on Nov. 10th.  HELP!!!

[LAYNA]

MY FRIEND LET HER SON WEAR HIS UNDERWARE OVER HIS DIAPER TILL HE PROVED TO HIMSELF THAT HE COULD DO IT AND SOON HE DIDN'T WANT TO WARE THE DIAPER ANYMORE.  IT WORKED SO WELL SHE'S DOING THIS WITH HER YOUNGEST SON NOW!