Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh and Ramadan Mubarak

Wearing Hijab is an act of worship in obedience to Allah. All acts of worship have exemptions when it comes to medical matters that can be harmful to the person. From what you described I have reservations on this doctor you saw because he missed the whole diagnosis in the beginning! So I am not sure if his later diagnosis is sufficient as the Hijab is the cause of such thing!

My suggestion is the following:

• Check with another physician to really verify if the Hijab is a cause or not.
• See if fabric that Hijab is made of like silk or such can help when wearing instead or removing it totally.
• See if treatment can be taken and I am sure now with medicine so advanced that there must be something to use for cure without need to remove Hijab in public.
• If you are to use a wig then you must still cover.
• Try to limit your presence in public so you can be without Hijab around either female of people who are your Marham.

Almighty Allah knows best.