Baby’s not sleeping

So it’s 3:30 am. I’ve let baby roll, cry and whimper for an hour now. Initially he woke st 1, then I got him down. He woke at 1::30 then I got him back down. Woke up at 2:30 and still not drifting off. My daughter never had these issues falling back asleep in the middle of the night so this is killing me. I can’t feed him to sleep, he doesn’t keep a paci in his mouth, he’s never been ok sleeping on his back, so I have to get up and walk him around. I’m just so frustrated night after night and I’m trying to keep my composure but I feel like I’m breaking. I’m having a hard time focusing at work from the lack of sleep.