I can definitely relate my friend! I have a six year old boy (he'll be seven late October) and within the last six months I'd say, he is staying dry at night. I went through the same things: no matter what he'd drink/not drink, he'd still wet the bed. At first, I thought it was because of his allergy medication he'd take at night. But once he was off of those, he would still sleep so hard you could drop a bomb next to him and he wouldn't wake up! So trying to take him to potty when I went to bed at about 11pm wouldn't help either. Sometimes it would make a difference, sometimes he'd end up wetting the bed anyway. Needless to say, it was a very challenging time for us: we couldn't find any rhyme or reason to his bed wetting. He just wouldn't feel it and wouldn't wake up! All of this to tell you that one day, it just clicked! The pediatrician told me the same things that your doctor has told you, and many of my friends said the same thing: just wait. After seven if it's still going on, then we can talk about it being a problem.
My encouragement to you is that someday, it will click for your boy too! It just clicked for my son one day, after many many many months of wetting for no apparent reason! He went from completely soaking the bed and letting all of the pipi out in his bed, not even feel it or know he had to go, to feeling the pipi and having minor accidents in the bed and then doing the rest of the pipi in the potty, to now he has the occasional little bit that comes out in his underwear before he makes it to the potty, but no wetting of the bed or sheets or even his pj's. What I do now is: I don't give my son soda or juice late in the day. He has half a glass of water with dinner, before 6:30pm. Nothing else to drink after that. And he understands and we remind him every so often when he'd like more to drink, etc. "Son, if you want to stay dry, we can't have a lot to drink at night" and he's taken ownership of that and wants to stay dry so he complies very happily! Because I limit what he drinks at night, during the day I give him lots to drink, whenever he wants! So he's not thirsty at night because he hasn't had enough during the day...Every child is different, so try different things to find what will help things "click" for your son!
One more thing, I found that the training pants at night prolonged the process. There was no incentive for him to stay dry, there was no discomfort to him. He wasn't wetting his bed, so everything was cool. I know it's a pain, BELIEVE me, changing urine-soaked sheets is one of my least favorite things to do!!!!! I dreaded every morning when I'd have to do it. It gets old SOOOOOO fast....But, there's something about the discomfort of them feeling wet that helps to train them. Can't explain it, but I'd encourage you to try and stick that out for a little bit. I know it helped us. And just talk to him a lot, encourage him. Tell him you love him no matter what, whether he wets the bed or not. I would just talk to my son, explain that it's okay we had an accident. Tomorrow we'll try and get up when we feel the pipi needs to come out. You know how when you have to do pipi during the day you feel the pressure, same thing at night. We need to learn how to feel it at night. The more we talk about it with them, the more it helps them realize it and internalize the need to wake up at night. And us waking them up when we go to bed, and them feeling the pipi on their clothes at night - somehow it all works together!
Sorry for the incredibly long response, but when I read your request I just wanted to encourage you!!!! This is very fresh for me so I can so relate to your struggles. If you ever need to talk, my email is ____@____.com
"This too shall pass..." my friend, so keep the faith! Be encouraged, you can do this!
: ) Becky