D.,
I have not had this experience myself, but over the years I have talked to several moms who were concerned about their children who complained of severe stomach pain. They couldn't go to school, play, or do any activities. It affected every aspect of their little lives, but the doctors could not find anything wrong. Eventually, both families realized that it was due to stress. The little girl was in 3rd grade when she was experiencing her problems. The little boy was in 2nd grade. It's very difficult when the children are so young and can't be more specific about what type of "hurt" they are experiencing, exactly where it hurts, and possibly narrow the hurt down to certain times of the day or after eating certain foods, etc.
The little girl's mom and dad were having marital problems during her pain. They thought they were hiding their conflict from the children, but Whitney could sense the tension, and it was affecting her health. After the problems were "resolved" her pain stopped immediately.
The little boy in the other family has a type-A personality, and would get extremely stressed out at school if he did not make 100's on every paper and be the best at PE or games or whatever. After this stress was taken away, his pain stopped.
Even though the pain these children were experiencing was brought on by mental or emotional stress, it does not diminish the reality of their pain. They were suffering true, extreme physical pain that could not be taken away with medication or surgery or whatever.
This is just one thing to keep in mind. A couple of other ladies mentioned something similar to this as well.
Others have mentioned Chrone's and other gastro problems. This is a good possibility. My mother-in-law and my husband both have gastro problems. Their pain is severe as well when they eat things they shouldn't. (They don't experience vomiting, though, they have diarrhea).
Others who have responded to you have mentioned possible female problems. Several female members of my family including myself have suffered from endometriosis which is can be a serious problem. If this is a possiblity, PLEASE get it checked out. However, if she hasn't started her period yet, this wouldn't be the problem. Maybe some other female issue?
I will also throw in this comment from personal experience. My children and I love our pediatrician. And when it comes to viruses, simple infections, and stuff, he's right on the mark. However, my children have experienced problems that ended up needing specialists to resolve. If I had not pushed the issue, the pediatrician would have kept "blowing it off". That sounds more uncaring than I mean it, but it took me insisting on him referring a specialist before the problem got resolved.
We will pray for you. Trying to help your children feel better without success is SO frustrating.