My 6 month old doesnt sleep

My son used to sleep from 6pm till 6 am with only 1 wake up call, at 3 months he went into his own room, he now doesnt sleep, he sleep for 20 minutes if im lucky! Ive tried taking back in my room, dream station, naturcare relaxation, sleeping bag, duvet, blankets, different night lights, extra food, controlled crying, you name it ive tried it, in 3 months i havent had 1 full night sleep! I need some sort of help, health visitor is out of options, doctor is out of options, during the day he has 3 20 minute naps and is happy and barely cries, but as soon as night time comes just constant crying! Please help! I will try anything except putting him in my bed!
Its starting to effect my every day life as im drained and tired