Why won’t he sleep!!

I can't for the life of me get my little one (14 months) to go to sleep, at any given point, he fights his naps during the day, like really fights, screams to keep himself awake, bedtime comes and he's been awake all day yet he just will not go down to sleep, I've tried sleeping bags, white noise, bottles, cuddling in, walking around, sitting in bed next to him, he just will not give in and sleep! And if he does, he wakes up almost instantly, eventually he caves around 1/2am after around 16 hours of being awake, I'm at a total loss! He's not in pain, I give him stuff for his teeth and I have tried leaving him to fuss for 10-15 mins but he just gets hysterical, it's been like this for almost 2 months now, we've only had 3/4 nights of solid sleep in that space. Do you have any other help or tips that can help me out here? I've asked family and no one is willing to take him for me to actually get a sleep haha, I just need him to go to his bed!! He used to be an amazing sleeper, from 5 month he’d sleep 12 hours solid every night in his own room no issues at all! Does anyone have any advice or been in this situation?! What did you do? What helped! I am desperate