Have you had him checked medically, my DS2 woke every hour or so at one stage, he was happy as anything in the day, but wouldn't sleep at night. Turned out he had an ear infection.
My DS1 also showed almost no signs he had glue ear, he was a bad sleeper and it was a combination of enlarged adenoids and glue ear that lead to poor sleep... essentially a form of sleep apenoa. I don't want to denigrate Drs but many just fob off with a try controlled crying, when often there is an underlying problem they aren't specialised enough to see. Took an ENT to find my DS1s problem...two GPs said his ears were clear, ENT said they were full of clear fluid, but as they weren't red and bulging the GPs didn't pick it up...ENT told me it wasn't uncommon to be missed