H.A.
Hi there,
My little one is almost 3 and has been potty trained for over 6 months, but has some quirky habits that come and go, and she sometimes holds it. I'm guessing it's typical at this age and at the beginning of potty training.
I do know that she's very afraid of the automatic flushing toilets and the hand blow dryers. So I always put paper over the flushing sensor on the toilet and we never use the hand dryers. Can you ask your son if he us afraid of something?
Also, as with so many things with little kids, I've found hat their learning is not linear, meaning that just because he was doing great for a month doesn't mean that you won't have unexplained setbacks. But that also doesn't mean that he'll never use the potty just because he doesn't want to now. (obvious, I know, but I helps to remind myself of this when we have a step backwards :) It takes a lot of patience, but just hang in there.
H.