toddler waking in the night...

ever since our little one started living with us she never had an issue sleeping. she had always slept through the nights with no issues. But the last couple weeks she’s been waking up in the middle of the night crying. (Not every night but more so then not). She’s perfectly fine when we go see her and she’s fine when we leave the room for a few minutes until she starts again. We check her diaper and change it if needed, but most of the time that doesn’t help. We usually just have to let her cry it out until she falls asleep again. What could it be? Should we be trying other things?