We have the same identical issues! My son just turned 3 a couple of weeks ago, and I started potty training a few days ago. He was peeing in the potty the first day, and hasn't peed in the bed YET since we started. He will hold his poop also, and cries for a diaper so he can poop (which I have refused).He is very regular and now he's pooped once in 3 days (and that was in his undies). Taking him to his Pedi Friday, hopefully will get some good advice soon. So scary knowing that this it dangerous for them to hold it. I'll pray for ya hun, and let me know if you make any progress, and I'll do the same! Good luck!
Make sure you are giving him plenty of fiber, so his stools are softer and don't hurt. Have you tried letting him see your's in the toilet. This helped our dd when she saw it didn't hurt me...Also, a tablespoon of dark karo syrup will help with constipation.