why is my scalp itchy and sore?

[fee24fee]

I have very itchy scalp...it's very sore when I touch it and when I scratch it....it itches so bad that I can't help but to scratch My head. I try to scratch as soft as I can but it very tender.  The itching and soreness is only in the middle of my head . The crown area..my hair is thinning a little in that area and it kind of feel a little scaby; but I can't really tell. 
I am a 24 year old female. Black African American. 
I don't take no medication. No known family history of This issue. I haven't got my hair relaxed in almost three years.all of my hair is natural now. Before I stopped getting my hair relaxed ;my scalp was itchy but not as bad... now it's terribly itchy sore and even when I shampoo my hair.  I shampoo my hair once or twice a week now.  What could this be? 
Thank you

[GinaJohnsons]

Stop using hair products which contain chemicals, this will make your condition worse since chemically-derived products often causes skin irritation. I suggest you switch to safer and organic hair products.

[PMDER1]

see a dermatologist