T.S.
My 5 year old son Alex was almost 3 when I finally got him to go on the potty all the time. I would let him run arouns naked while we were home, we had some accidents and I found Natires Miracle ( for puppy accidents works really good for little boy clean ups). I got tired of the diapers and I was pregnant with my second child at the time. I woke up one morning and said ok this is the day we stop using diapers because you're gettign to be a big boy now and you need to wear underwear. He was hesitant at first but then went and got his underwear and put them on. Within the first week we had 2 accidents adn then that was it. At night we use pull ups still, and we still have the occasional accident now at 5 but we're working on that one now too.
Good luck - what the doctors say is true ..they will go when THEY are ready.