Okay, I need some advice... my 21mo old daughter has slept through the night since she was 5 weeks…

Okay, I need some advice... my 21mo old daughter has slept through the night since she was 5 weeks old... unless she was sick or teething... the last couple nights she's been waking up at 3am... takes about 20 minutes to get her settled back in and back to sleep... she's also been fighting her nap and at bedtime... just wondering if anyone else has had these issues... could she be cutting more teeth? She currently has 12 teeth... I'm just SO tired! I don't know why she's not sleeping!