Maybe he's just not ready?
My son was wet everynight and we were all stressed out trying to force him to be dry.
We became more laid back about it. And he literally went from wetting the bed every night one week, to wetting it 2 nights the next week and staying dry the next. It was just like a switch went off and he figured it out. This was around 4 1/2. He's only wet the bed once or twice in the last year and a half. (Now he "wakes up" and sleep walks and pees in the hallway sometimes).
A few things we did try, not sure how much it helped...
Limiting his fluids 2hrs before bedtime.
Waking him up one time 2-3hrs after he went to bed (when we were heading to bed).
Letting him pick an item from a prize box each morning he was dry ($1 toys - usually matchbox cars).
Also, we took him out of his pullups at 4ish and let him wet the bed. (We tried this when he was younger and he would still sleep through it so we put him back in pullups). I was changing his sheets at 2 am every night for a while. But he was waking me up and telling me to.
For these frequent sheet changes I'd actually have 2 fresh sheets on the bed so that when he wet one I could pull it off and the bed was already ready to go.
(mattress > mattress pad > plastic sheet > fitted sheet > sheet > plastic sheet > fitted sheet > sheet). I just had to wip off the top sheets and the top plastic sheet and there was a fresh one already there. Job done.