My teenage daughter has a rash on her upper arms (inside) and parts of tops of legs, inside & out. It seems to improve, then worsen for no reason. Her arms ache too. We have eliminated allergies etc. she has had a blood test & urine tested, all came back clear. The spots are red, some purple, small, not raised. She has no other symptoms, but we would like to know the cause. Please can you help?