What Could Causes Sudden Darkening Of Skin And Itchiness All Over?

i am a 50 yr old female of about 75 kg wt and 164 cm ht.
My skin colour is wheatish.......
But recently after taking something which i dont know ,my face turned jet black with lot of scales, dryness, ugly....
I am having itching all over the body..
I used several medicines for this after consulting dermatalogists but none of them worked for me......
Please tell me the reason for my condition and advice me how to proceed further