B.C.
I think this must just be a phase, because my daughter, who is almost 15 months, just went through this too. But now, she's back on schedule and doing great. She was down to one nap a day, which she wouldn't take until she was just purely exhausted at about 5pm!
I just kept laying her down at her normal time everyday, and made sure that her tummy was full. Eventually, she just gave in and started sleeping again.