Hi T.,
I understand your frustration! My 3 yr old daughter regressed to wetting her pants about a month before her brother was born, and then again after he was born. Recently, when my brother and his wife had a baby, she did the same thing. My answer was the potty watch. It is a simple watch your son will wear but it has a timer that you can set to sound off every 30, 60 or 90 minutes. What's great about it is that it resets itself and it goes anywhere with them. You don't have to give a long explanation at daycare or anywhere about what's going on and this is what you have to do. You just put it on and ask whomever is caring for him to take him potty when the music goes off.
We started out with the 30 minute interval until we had no accidents for two days, then 60 minutes, and then 90 minutes. She started telling me again that she needed to potty or just went herself, and that was when I knew we could retire the potty watch.
You can find them online for about $10 at www.onestepahead.com and a friend of mine told me she found one on eBay. Definitely worth the price. Good luck to you!