I am not familiar with lupus but I do have allergies to certain chemicals and preservatives that give me dry, itchy, rashy skin so I can relate. I am not a Dr and can only speak from experience with my own skin. You're best bet is to get the condition formally diagnosed.
That said, I know everything you've tried is what is reccomended here by other curlies but NONE of them will moisturize or heal itchy skin:
-Hot Oil treatments, Pure Moroccan Argan Oil:
Oils DO NOT provide moisture, they can only seal in moisture (water + emollients) that was previously applied. Some hot oils may be made from penetrating oils and protein and may help the hair but I'm not sure how this would translate to the scalp.
-Tea Tree Oil (the oil and the shampoo), peppermint, menthol, etc:
Some of these have antiseptic properties. All cause a tingling sensation that tricks/distracts the itch/pain receptors in your skin, this is a temporary result. All are known sensitizers and can lead to worse problems later (this was a lot of my issue).
-Brown sugar scrubs:
This is the same as scratching a bug bite, it damages the skins natural barrier and causes more damage and can also release more histamine to the area which causes more itching (if cause is allergic/inflammatory).
If you actually have dandruff this may help, however most dandruff poo's contain SLS and other harsh ingredients. If you don't have dandruff, it won't help and may make the issue worse.
Going CG with the right products should help; try a water-based cowash with emollient ingredients and few oils/butters, something with some protein may help too. I personally feel its best to avoid the mainstream, chemical laden products in favor of more natural brands. However, many 'natural' ingredients are sensitizers too and could cause dryness, itching.
Your best bet is to educate yourself:
Paulaschoice.com has an ingredient dictionary, Cosmetic Ingredient Dictionary A - Z: Cosmetics Cop Expert Advice
, and lots of great articles on skincare. She is not CG
but she knows about skin issues (and your scalp is skin), most of what I've detailed above I learned from reading through her site and it has absolutely helped my skin issues. There are many other ingredient websites if a specific ingredient isn't listed.