Copied from coeliac uk website:
Symptoms of coeliac disease may range from mild to severe, and can include:
Bloating, diarrhoea, nausea, wind, tiredness, constipation, anaemia, mouth ulcers, headaches, weight loss, hair loss, skin problems, short stature, depression, infertility, recurrent miscarriages and joint/bone pain.
DD's cousin has also recently been diagnosed at the age of 12. He was refusing to go to school, mainly because he felt so ill and tired all the time, but I think he also had behavioural issues which have improved since his diagnosis.
BeeEm, when I found out about DD1's coeliac I was almost pleased - I was finally vindicated and I was not simply a neurotic mother and she was not simply a fussy eater, but there was something wrong with my child. I had been given the complete brush-off by all the medical professionals I'd seen since her problems started, which with hindsight was about a month after I introduced gluten into her diet when she was being weaned. I bow down to all the mothers who deal with far more challenging dietary issues in their children and am grateful that following a gluten-free diet is relatively simple and if she does eat gluten by mistake as a one-off, it is not life-threatening.
It is horrid to know that there is something wrong with your child but not know how to put it right. I hope you get some answers v. soon. In the meantime, if you need any more information (GPs are notoriously badly-informed on coeliac) don't hesitate to ask.
BTW, I am no expert on coeliac, I only have my own experience to go on and as others on this thread have said, your DD's symptoms can point to a number of things. But if you can eliminate this one thing with a simple blood test, then you can start looking in other areas. Best of luck.