We went through a difficult time around that age. Primarily because of teething and also because Riley began to transition to one nap. I knew it was time because in our case, his morning nap got longer, resisted the pm nap and bedtime, had more nightwakings and got up earlier. For a long time we were in that frustrating stage where one nap was not enough and two naps were impossible to get. On those days I offered a catnap in the morning and an early bedtime. Over time, it has evened out and now at 16 months, our schedule is as follows :
7-8: wake
12-2 or 3: nap
7-8: bed
It has been that way for the last month or so, I'd say. There is a thread about the 2-1 nap switch,, you may want to look over that for ideas. HTH a little