More allergy testing....

So since Ambers had an upset stomach (diahorrea) for months now we had to visit the dietitian today and give a list of things we think it could be, with her reaction the other day I thought wheat or soya and she also gets a terrible rash off tomatoes! A few people have suggested gluten could be a cause for this too so I took my list and food diary up. We were told to just take her off everything to give her stomach time to get normal again! The paediatrician is going to send us word for skin prick tests and then it's just a case of introducing one by one.....I think we have a long journey ahead..... Now egg free milk free wheat free gluten free soya free tomato free Amber Rose..... (Help!)