17 Month old randomly won’t sleep through the night 😩

I’m 32 weeks pregnant with my second. My 17 month old randomly is waking in the night. He falls asleep around 9pm and wakes around 3 and won’t fall back until around 6, no matter what I do or change! Could it be a sleep regression?! Oy I’m exhausted 😫 I’ve tried shortening his 1pm-3pm nap time to just 1pm-2pm...I’ve tried eliminating screen time...... I’ve tried having him get more energy out..... I’ve tried making sure he is full of dinner 30 mins before bed.... and always the same. At a loss.