Chronic Itching

I have had chronic itching in my feet (starts in the heels and moves forward along sides and bottoms of feet).  This has been going on for many years, comes and goes, and it seems to occur when I am in bed and when my feet get hot.  It has driven me crazy.  I have seen a dermotologist who told me it was probably some nerve issue as there is no rash or fungus, etc.  Lately I have started having itching in other parts of my body.  Last night I slept horribly because I itched from head to toe.  I have slight itching during the day.  Any clue what this might be?  Thanks!

Mickey