My son also had trouble with wetting the bed and no memory of doing it. Due to other issues, we were seeing a pediatric urologist. There are some urlogical problems that can be assoicated to bedwetting. We ruled those out and learned that this is common with boys. It can become worse (more frequent) during a growth spurt. Some measures you can try to help . . .
1. Cut fluids 2 hours before bedtime.
2. Make sure he isn't constipated. This could be the case even if he poops regularly. The pressure from the constipation can contribute to the bed wetting.
3. Set a timer to take him potty every 2 hours during the day. An overstreched bladder from waiting too long during the day can reduce the sensation to go during the night.
4. Take him to the potty 2-3 hours after he has gone to bed. If he doesn't wake when he wets, he probably won't even remember getting up to go. We had to carry our son to the potty every night until he was 7 1/2 years old but were told it could last until pre-teens. We found this the most effective measure to keeping dry through the night.
5. Don't let him feel bad about wetting the bed because it's not his fault.
6. Our issue continued into the time he started going for sleepovers. I just asked the other mom to get him up before she went to bed and we never had an problem.
This is a simplified list of the measures we took. This issue resolved itself for us. Good luck.