What Causes Burning Sensation On The Back, Armpits And Genitals?

I have burning sensation on my back for the past 8 m0nths. Now i have the sesation in armpit and genitals [outside] Here and there over my arm knee and breast i get irregular patches with a needle prick at the centre and it gives burning which lasts for a short time I am deeply worried if it might be a serious skin disease