Please post if you found anything out. I'm having the same problem with my 3 yr. old daughter for a couple weeks.
For the critics that browse around:
No, I haven't made a doctor appt. because she's always fine during the day.
Maybe she is having reflux problems...People can be fine until they lay down and then there is pain. How does your daughter describe the pain and where is it? I would see a doctor about this, if it is reflux, there are meds that can be given to help her out and prevent this. Either way, she needs a thorough examination by her pedi. I hope you find answers...I wish I could offer more, but that is all I can think of...Sunny