So has he had an accident without the diaper on and doesn't like the feel of it?
I put them in those thick pull up underpants (waffle weave), no pants, or even naked if outside. I had a potty right next to them - I brought it around wherever we were. The minute they started, on to the potty they went. Mine hated the feel of pee or poo. It didn't take long at all. It just meant a couple of days at home (I picked a weekend that worked for us) and was consistent.
But if he's upset and screaming for his diaper, maybe he's not ready. Trust your mom instinct on this one. Mine had just turned 3 and were ready but not every kid is.
Keeping the potty close by was what worked for me. Once they knew the signs and could hold it long enough to get to washroom, we moved potty in there and then did the potty ring on toilet.
Good luck - it will come. Everyone goes through potty training challenges :)