Hi!
I went through the same exact thing recently and you might need to adjust your schedule. By this time, he would be on a 1 nap a day schedule, so if he naps at the sitter, most likely he will not nap at home. I had to push my naps from 12:30 to later in the afternoon around 1:30. They only nap for 1 hour, depending on how much we play that day. I also make sure we play, and no tv. Even being outside for 30 minutes riding the bike up and down the street even tires them out. I also kept my bedtime routine the same. (potty, prayer, kiss, sleep music)
I know this is not much, but this is what I did. It took about 4 days to adjust them to the new schedule, but we are now doing it.
M.