Do you lichen? There are 4types of it And I have three. I have itching as well and have had for decades. Have you had skin testing done for chemical chemicals and foods like egg whites that could foam up and is used in many products. I’m very sensitive to egg whites and they are in shampoo, toothpaste soap.
It could be your shampoo you’re using also your water. I had to put a whole house filter as well as a softener in my house due to itching and sores throughout my body.
If you have skin testing done, they should check you for the chemicals they put in the water to make it safe to use.
I do have a prescription and it’s a steroid that I put in my hair every day and that does help.
I wish you the best and figuring this all out it’s not easy you take care