1.5 year old wont sleep at night

I’ve tried everything. I have a 2.5 year old as well and am 6.5 months pregnant with my third. My 1.5 year old never slept through the night and he is so stubborn he literally screams his head off for hours. And finally he’ll fall asleep and wake up 2 hours later to do the same. With my first we cut out milk at night and switched it for water and eventually he stopped waking up for it. That didn’t work for this one. He just screams and screams multiple times a night. He can go for hours. I’m beyond fed up and need to sleep and get him to sleep.

He only takes one nap during the day and not anywhere near his bedtime. Please help. I’m so tired.