My 7 year old has the exact same symptoms. I know this was years ago but did you ever get an answer?
My 7 year daughter started doing this Wednesday moght, has thrown up Saturday evening, and again a little while ago (Wednesday night). We have racked hr brains ans can't figure it out. We have follow-up with doctor next week, or sooner of we decide to take her to the ER. Docs thought it was caused by allergy reactiong but she has shown no other symptoms two of three times.
I would take her to the ER.