Hi T.
My daughter is almost 7 and still wears a pull-up at night! my neighbor has 5 children, and the 2 oldest were very slow to be dry through the night (their almost 7 year old still wears a pull-up too)
This is not that unusual, and can be less of a problem (sleep deprivation!) for you if you just let him outgrow it. My pediatrican offered suggestions ranging from drugs to behavior modification, to doing nothing and letting her outgrow it (his recommendation). He assured us that our daughter is still within the range of normal. He said that, statistically, there is probably at least 1 or 2 kids in her first grade class who are still wet at night too. I think among 5-yr-olds only about 50 or 60% are dry through the night (don't quote me, but look up the stats) So, your son is not alone! Many parents will still not even talk about it, because they think it is a stigma, when in fact it is totally normal developmentally! If a child has a small bladder coupled with being a very sound sleeper, you get a kid who still wets at night.(asuming there is no underlying medical issue, like a bladder infection)
If you want your sleep back, and a happier son and mom, I would try to take yourself out of the equasion by creating a situation where you are not required to wake him up to go.(you can't teach him to wake up on his own anyway, and he probably does not even remember that it happened!) The problem you have is to convince him to go back into a pull-up at night, which might be tricky. He may have picked up on your concern and frustration, since your first two did not have this issue. He wants to be big like his sisters, and wants you to be pleased with him! Talk to him honestly about his bladder and how soundly he sleeps. He is old enough to understand. Maybe you could try putting a lot of the responsibility on him to pick out what type of pull-up he wants to wear (there are some cool new types now that look like boxer shorts or pajama bottoms), to change and clean himself up, and to change into "big boy" underwear in the morning. Try to convince him that it's nothing he can control until his body grows, which is the truth, but he CAN be a big boy by dealing with the situation he is in right now. Since it is already a negative issue in your house, I would give him some big-time "Big Boy" rewards for wearing the pull-ups. My daughter is starting to be dry on some mornings, and we try to give her a lot of praise, but not draw too much attention to the whole topic, since it has not been a huge negative issue in our house. She does lament once in a while that she wishes she were dry all the time, but we just try to be positive, and assure her that it is normal, and when her bladder grows, she will be dry.
I would discuss this with your doctor, and look in any Childcare books you can find. (T. Barry Brazelton is my favorite, or Penelope Leach)I know how you feel, though! My older son(almost 16 now) was dry at night when he was around 3 or 4, so at first I was wondering what was going on with my daughter (plus, I think this issue is more common with boys, but I had the opposite experience!) Like they always say....none of them goes off to high school in diapers! So, try to relax and let nature take it's course. He will be fine! PS: Restricting liquids does not really help, and just makes the child more negative about the whole thing...I mean, I wouldn't let him drink a big glass right before bed, but don't get overly focused on that. Good Luck