9 month old doesn’t sleep

Hi all, bit of a write up but this Mumma is EXHAUSTED! I’m a mother of 3 kids, 7years and under. I’m having absolute hell with my youngest who is 9months old. From about 8 weeks right up to 6 months he was a dream when it came to sleeping, mostly slept through the night or on occasion have a feed or 2 during the night but otherwise fairly breezy but since 6 months right up until now his night sleeping is hell. He wakes every hour and takes up to half hour to get back to sleep and then is awake for the day at 4:30-5am so I’m averaging on 4 hours of broken sleep most nights. He is like this more often then not with occasional win of a sleep through (rare but does happen) he’s a happy content baby during the day so he’s not in pain or unwell. I have tried EVERTHING I can think of with no luck! 😭 and advice would be incredibly helpful. What I have tried so far is: putting to bed earlier/later, less sleep/more sleep during the day, feeding during the night, let him cry which ends in him vomiting, belly sleeping/back sleeping, giving Panadol/nurofen incase he’s teething, more solid food (he eats like an absolute trooper has 3-5 meals a day with no allergies or food sensitivities), lavender oil in his bedroom, night light on/off, keeping to a strict night time routine, dummy. He normally goes down around 7-8pm and the waking begins from around 10pm through till 5am. I’m to the point where I can hardly function anymore and I can’t rest during the day with my 3 year old home and I also work part time.