Toddler keeps waking up in the middle of the night

For the past three nights my 17 month old has been up for 2 hours or so in the middle of the night. When I say up I don’t mean ready to play though, I mean I go in there to nurse her back to sleep and then she falls asleep and wakes up and falls asleep and wakes up. Over and over again for hours.

She’s never had any problems with teething so far in her life so I don’t think that’s it.

Any thoughts as to what it could be and how I can make it normal again?