What Causes Stomach Ache And Vomiting In A Child?

My daughter is 6.5. She woke at 2:20 this am with stomach pain. She eventually vomited. Food came up this time, but she has done this in the past. Roughly a year ago, she woke, stomach pain, vomited, then felt fine the next day. No fever, etc. she did this a few months back, same exact way. Then again about 2.5 weeks ago, now tonight. In the past she has thrown more mucus than anything, tonight was more food. In the past I knew she never had a temp, but I cannot recall what her temps were. Tonight it was low, 95.7 under her arm. That maybe equates to roughly 96. I am concerned with the low temp. Originally, I was thinking she got a sour stomach from too much food too close to bed time, or too many different types of food, etc. now I am not sure as the frequency is more and now the low temp thing. She is on a gluten free diet for excezma, rashes. Apparently she was a wheat allergy. It was never tested, but we tried removing gluten and her rashes went away. She has been gf for 2.5 years now. We are very careful, I reviewed her foods for the day, I doubt any cross dontamination happened.