Well, if it makes you feel any better, we've been going through this since Tyler was 20 mo or so (he's 22 mo now, so maybe it's been even longer...sheesh, I don't know!). He takes his nap about 75% of the time now, and when he doesn't, he happily plays in his crib or practices his wrestling moves on his teddy bear. Those are early to bed days! It doesn't matter what time of day I put him down, if he doesn't feel like napping, it just doesn't happen.
I think (HOPE) it's a phase, because I'm not ready to lose that nap yet! I don't think it's teething here, he hasn't been chewing or telling me his mouth hurts. I just try to go with the flow as best I can!