Yes, a urologist may be a good idea. Also, it's possible that it's psychological. Around the time his problem got worse, did anything happen? Has he had any trauma in his life before that? Any stress? Is your home low-stress or high-stress? Kids feel all of it and know what's going on, even if you don't talk about it in front of them. It doesn't even have to be about him.
I'm glad you don't scold him about it anymore. I'm sure he feels bad enough about it, already. Just make sure he knows it's not his fault and this happens to a lot of kids. If you or his father used to do this, tell him that (but don't lie). Make sure you find reasons to praise him when he does things well, so he can build some self-esteem outside of this issue.
When you go to the doctor, make a list of all the conditions that can cause this--do a little online research. Go down the list with the doctor and make him consider each one (UTI, diabetes, bladder infection, etc). Also, make a list of treatments--ask about medications that may help (especially to take just for sleep-overs). Your son can even be playing out in the play room when you're having this conversation, so as not to scare him. If you don't get any answers, then go to a pediatrician or a specialist (the doctor may be able to recommend someone).
Don't let the doctor dismiss this as just normal bed wetting. Remind the doctor that he's having problems during the day now, which shows that it's not just a problem of not waking up in time. Maybe he's not feeling his bladder like he should. Or maybe he has developed an infection. After all, kids who wet the bed can get infections, too, which may be dismissed as just normal for them.
Good luck. I really hope you can find a solution quickly.