Hi ! I have gone through your question and I understand your concern.
As I understand you have itchy
scalp and hair loss only when you have head shower , right ?
Does it start immediately after you have the shower , and it last after you finish your head shower ? -- If thesese question are yes .I would say that you may have
contact dermatitis caused by your hair product you use such shampoo, or other cream .You scalp seems like is very sensitive to a product .You can find out wich is by stoping then one by one and see if it dissapear.
The hair loss is caused of your itchy hair and once you will not have more itching ,the hair loss will go away .Once you stop the cause of itchy hair , you will not have more hair loss and you hear will be back to normal .
In this case I would recommend you to use natural hair product , don't pull your hair while you wash them .
Hope these help
If you have any other questions please feel free to ask me
Ovoid was , hair spry