My Teenage Son Isn'T Potty Trained

I'm going to tell you something and I'll be quite plain. I have a fifteen year old son who couldn't be potty trained. I tried to potty train him but I wasn't able to succeed. He still wears diapers because they're what he needs. The kids make fun of him when he takes showers at school. They laugh when they see his diapers, my son truly is a fool. He's not even smart enough to change his diapers, his gym teacher and I have to do it. Using protection on the night when he was conceived would've been wise but I blew it. The situation is so embarrassing, what am I going to do? I really hope and pray that other people aren't in my shoes.