S.,
Oh how I remember this! The potty power struggle. In all likelihood, your son knows that you really want him potty trained and realizes he has control over something you care about (usually it's the other way around, right!). He does not want to give up that power. I ended up in a power struggle with my son about this when he was 3. After reading books, calling into a radio show about having power struggles with kids, etc., we took a break (i.e., put him back in diapers) for a few months (though you might not have time for that long a break) to break the cycle. Then one week we let him know that, at the end of the week, there would no longer be daytime diapers at our house (you would have to say "in his size" because you have a baby) because we had no one in the house who needed them any more. Then we had him go around w/out pants (which he hated) and made sure there was always a potty in the room and that he knew where it was. He wanted to try with his pants on first, so we said sure, we'll try it your way first, and if it doesn't work then we'll try without pants. We tried to sound very matter-of-fact. He peed in his pants about 20 minutes later, so pants off it was. He cried, but we just said one time, "This was the agreement we made," and let him cry. We also had a sticker chart with stars for pee, balloon sticker for poop (he loves balloons and those stickers were larger), and gold star stickers for not complaining about going or for asking to go (and then successfully going!). We had him help make the chart so that he felt included, not like something was being done to him. We also had small prizes -- one for the first time using the potty, another for a week with no accidents, etc. When he first used the potty (he had actually been using it fine about six months earlier and then regresses -- even longer story), we congratulated him and clapped, hugged, etc. After that we just smiled, said great job, and let him put up his sticker because he needed to understand that he was expected to use the potty. Some people I know kept the prizes high up in the bathroom within eyeshot of the toilet. We also took him to the potty every 45 minutes for the first couple of weeks, and made him stay on it for three minutes (fun egg timer helped). We were told to do this because it can take kids a bit to relax and go and/or completely eliminate. There were also weekly activities that our son loved to do (like music class). We told him that, sadly, those places did not allow people who pee on the floor into their places. Unless he could go without an accident the day before, we would not be able to take him to the activity. We explained that we couldn't do anything about those rules, and that we knew he could do it. When he had an accident, we did not look or sound upset, just disappointed that now he wouldn't be able to do the activity on the next day. Yes, this punished us a bit, but it was way better than the potty struggle! When the next day came and he realized that he really couldn't go to the activity, we held him when he cried and let him know we were so sorry that the place had those rules. Then we reminded him that the activity the next day had the same rules. If he could get through the day without an accident, he would at least be able to go to that activity. Again, we expressed our confidence in him. And that was it. No more accidents. We have had one (maybe two?) in the 1.5 years since then. I think it really helped to have natural consequences for not being potty trained as opposed to ones that seemed to come arbitrarily from his parents. Also, don't bother with undies at first if that's a barrier. Just let him wear sweatpants. Try a break for a month. It really did not take more than a few days once the power struggle subsided (we kept up the timer for about a month, though). I wish you the best! K.