Night Bedwetting - 5 yo boy

Hi,
My son just turned 5. He was fully day toilet trained by 2 1/2 yo. I was hoping he would grow out of his night bedwetting by now. He wears a nappy/pull up everyday and it is wet, full in the morning and sometimes it even overflows. I can count the times he has been dry in these 5 years on my fingers.
Have tried leaving hime without a nappy too but he just gets wet and will lie in it for sometime or the whole night without realising he is wet.
He does want to stop as he feels he is a big boy now but gets disppointed when he wakes up wet.
He had his tonsils and adenoids taken out last Dec. Everyone said it would settle after that but hasn't. He suffers from hayfever. If he is awake he will get up and go to the toilet but when asleep no. No fixed time to wet the bed. Does not drink anything after 7pm except if thirsty.
Please help!