Okay first of all, I am sorry you are going through this because you are pregnant AND have a 3 yr old on top of your 25m old. Aiy yai yai. :)
My 2.5 year old has gone through 2 stages . One @ 2yrs old & now at almost 3 years old. At 2, he stopped napping. That didn't last long. About a month. He's doing it again and he's very active so I didn't get it.
No molars. Don't think it's a growth spurt. So I have just been trying to roll with it. I know, I know it's hard. Ugh. The good thing is we did get back on track for awhile and I anticipate we will get back there again.
So you're not alone on the sleep changes.
Not sure that I'd wake him now. He's sleeping because he's tired. Waking him might make him not only grumpy but that has backfired on me. I'd think he'd be tired & get back on track just to find out I was wrong.
I feel like every day is a different day.
I do try and "tire" him out by encouraging him to be active inside & outside (weather permitting).
You could try waking him this time today and see how that works out for you.
I'm sure he's scared. Mine did this waking up throughout the night at that age and I think it was possibly some teething (molars) and bad dreams waking him up scared in a semi-dark room wanting his mommy. I made sure he had a nightlight and I'd go in there. I'd sleep in the rocker on the floor on a makeshift bed (comforters, blanket & pillow).
Hang in there, go in there to soothe him or have hubby do it & this too shall pass. Good luck sweetie!
Edit: I like what Patty said "never wake sleeping babies". That's what my instinct says & a friend told me that when he was little. I say try & roll w/these changes for now. Sorry but thought better of it. :)