I know the frustration it may cause, having this situation, not to mention how your son feels. I have a 12 year old grand daughter who is still having a bed wetting problem. My daughter tried everything, and one thing that kinda works when it is consistant, is waking her up, or at least walking her to the toilet, even if she was sleeping, helped. And making sure that she didn't have anything to drink or any sugarey products to eat at least 3 hours before she went to bed. She also makes sure she has gone to the bathroom before she lays down. She puts a plastic liner on the mattress too. Now, this is helpfull if it is consistant, and in my grand daughters case, that is not always so, cause my daughter works at night, and then my granddaughter forgets, and sometimes gets in my daughters bed, waiting for her to get home, and of course she pees the bed, cause she didn't follow the rules and precausions. But when the granddaughter does follow them, she is less likely to have the problem. They say she will probably grow out of it when she gets her period, and then it will stop. For boys, well, who knows. I have a 26 year who walks in his sleep and pees on any thing still. Especially if he had a lot of fluids to drink. I had a brother who peed the bed till he was 16 years old. He used to sleep with his cloths off, cause he didn't want them to get wet, and he would put a rubber sheet under the sheet.
So, I guess it happens to many people.
Good luck.