S.D.
Just an FYI, I have only 1 kidney, too. I was born with just 1, not sure if that is your son's situation or not. But I wanted you to know that it has never been a problem for me, at all.
With the potty training, he is still young, especially for a boy, so I would go back to diapers and not push him at all. Kids will potty train themselves when they are ready. We don't try to force our kids to reach other developmental milestones before they are ready, so it really bothers me how uptight people get about potty training their child. Give him a break, stop all together, unless HE suggests wanting to try.
Good luck
S.
(mom of 3 and daycare provider for 21 yrs)