What Causes Extreme Itching On The Back Of Legs And Ankles?

The back of my legs and ankles are itching like there is no tomorrow - I have used creams, lotions, rubbing alcohol, benedryl - etc - but it still continues - it is not ever night but most nights and they itch for hours - not always both legs at same time - it is to the point of scratching the legs raw - possible causes?