Sleep?! What is going on??

So I’m utterly confused and going crazy! My LO is 16 months old. I have her down to 1 nap a day (approx 2-2 1/2hrs) and at night she’ll wake once or twice but going back to sleep after a little soothing. But now for bout a week her sleep is so unpredictable! She’ll nap then when it should be bedtime, she’ll go to sleep, sleep an hour then be up for 3/4 hours! Or she’ll go to bed and then wake up at 3am and stay up till 4:30! Idk what’s going on but I am tired and on the verge of tears. She isn’t crying or cranky when she wakes so I can’t figure what’s cause this random behavior???