6 year old Female severe stomach pain.?

I realize your daughters very young but I have a Hiatal Hernia and Acid Reflux that's why I take Zantac 150mg. I too had this pain for 6 months from March to June of last year, the doctors ran every test including every blood test and nothing ever showed up. They said it had to be my Acid Reflux backing up in my stomach or something like that. I actually quit eating beef for awhile because the pain got worse when eating that it actually helped some not a lot though. Also could be colitis which is back up from colon not emptying properly. I've had that before with the pain in my belly myself. I hope this helps you out. I feel for you little girl I've been in her shoes.