Chronic rash

Please help. My daughter, an adult, is struggling with a very troublesome rash. It all started about two weeks ago with itching on the head, without a rash. After a week, a rash appeared on her arms and then on her thighs, buttocks, back. The rash is very itchy, so my daughter has not been sleeping for a week. She has consulted with several doctors. The current diagnosis is that they do not know what it is but there are more cases like this. There was suspicion of scabies and the appropriate ointment was used, but then it was ruled out. Allergic tests were done but nothing came out. Blood tests were done, including HIV, but they also did not show anything. Maybe someone from the community has encountered such a case and can help.