Baby would be sleeping throught the night but for....?

something bothering her every nite, like clockwork, at 3.15am. She wakes up and cries at exactly yhte same time every night. Im pretty sure its not for food as she doesn't fully awake, just lies there with her eyes closed crying. If i pop her dummy back in she will go off for 1/2 hour then wake again. She goes down at 8.30pm and usually wakes in the morning between 6-6.30am. She does suffer from reflux and Im wondering if this is what is causing her to wake. She has also been teething on and off. But the same time every night to the minute? just seems strange. Any Ideas anyone? She is 17 weeks