Debi-
My LO has been similar to yours very recently as well. I have been looking (like a hawk I might add) for the more subtle cues such as motor skills getting a little sloppy and slight lull in activity. Then I have been doing a longer wind down with sitting and reading. It seems that when she has really fun stuff going on around her, she doesn't want to sleep, but the reading, she will eventually become tired. If I don't see any of those more subtle cues, then I just "decide" when she should be tired and we go sit quietly for a while. It seems that once her limbs are not so active and she is quietly sitting, she will be more inclined to be tired and go to sleep. Our wind down for a nap went 30 minutes today.
HTH.