I hesitate to put my 2 cents in here because this might make your problem worse...but I have found when I have scalp pain that a scrubbing with a drugstore sulfate shampoo helps.

I really scrub - even though it sounds counterintuitive. I don't know what causes the tenderness in my case or why that works. I'm afraid in your case it might be a disaster but before you do a scalp biopsy it might be worth a shot. Sorry you are having this problem and please let us know how you are feeling!
2/c and some 3A. Modified CG.
Protein sensitive
Highly porous. Color over grey.
Best 1st day method: Super Soaker
Conditioners: Curl Junkie Beauticurls Strengthening Conditioner,
Deep condish: Curl Junkie Curl Rehab
Stylers: Mix Curls in a Bottle into everything for shine. Terrible pj
Sometimes try roller sets - classic glamor but I prefer my curls.
Every day is a gift