What Causes Constant Itchiness And Tenderness In Scalp?

Hello! I m an African American female my scalp itch all the time. I wash it once a week and oil my scalp every day but my scalp continue to itch especially at the crown and temple areas. In addition to, my scalp is tender and hair thinning in center top of my head. I don t understand why it itch all the time and hair thinning at the center top. I used everything over the counter and natural organic hair products to stop it but nothing work. Been to several doctors and Hair Club for help and the problem got worst. Please help!