Potty Training!

My son is 2.5. I've tried potty training before, but he wasn't grasping it, terrified of the bathroom, wasn't talking yet. Here's the thing, my son is speech delayed. He doesn't say more than one word sentences, and definitely won't say "pee" or "poop", we are working on trying to find the root of the problem, but currently potty training is hard when your child can't communicate when he has to go.
So today, I put him in some brand new undies with his favorite characters on them, and have been taking him to the potty every 30 minutes (and asking him if he has to potty every 10-he always says no). He's only had one accident so far, but hasn't gone on the potty at all, and when I sit him on he's trying to get back up. I've tried singing, reading his potty book, rewarding him with treats... nothing is working. Does anyone have any tips? I'm expecting baby #2 in 3 months so I don't want 2 babies in diapers. 😔