5yr old wont poo in the toilet without a fight grrrr :(

my 5 yr old son has been toilet trained (to wee) since he was 2
at the same time we started the poop training too
he let a bit go and that was it he was scared
now he is 5 and its just totally out of control
for the last year he has constantly been pooing his undies
3-5 times a day i change his undies
it is totally disgusting for both him and me :(
dont get me wrong he knows how to use the toilet
and has done so many times, but only when he wants to!!
i can beg him all day everyday and he will just go hide from me!! i have taking him to the doctors several times and they all just say it will happen in time!!
that is soo frustrating... because i am the one that deals with the poo in the undies (sometimes caked on soo hard)
i am the one that is sooo nervous to take him anywere or visit family because im scared he will poo
if someone says they are coming to visit its straight in the bath for him to get cleaned up so he doesnt stink :(
ive tried taking toys from him,tried bribing if u like to try and get him to do it everyday!! i tell him if u do it everyday then u get a toy at the end of the week
it doesnt work!! nothing does
its driving me crazy!! i no there is nothing wrong with him and that he is just sooo stubborn and scared for some reason
i put him in preschool/daycare to see if thay could help encourage him to use the toilet but that made it worse!!
now as i said im cleaning 3-5 poo filled undies a day
i just cant take it anymore
(but i have to )
he goes to school next year and i dont want him to go and poo in his pants and be the stinky kid in school
what am i doing wrong?
what can i do better?
anyone else having these problems?
anyone no how to try and get him comfortable using the toilet?
when he does use the toilet i have to sit right at the door and talk to him and make sure he does it!! its not very nice
anyways im just over the smell and the mess
my house smells yukkk and so does he (most of the time)
ilove my son and we have a very very close relationship and the way he trusts me is sooo awsome but i want a smell free child that i can pick up and hug with out worry about the smell
or worrying what other people think
he does care if he stays in the poo all day long it doesnt bother him one bit!
he will sit there and watch me clean his soiled undies as if its normal!!