I have several patches of dry very itchy skin around my waist. The patches are roundish and almost blue-black in color. The patches do not change much whether or not I am wearing something that rubs against the skin around my waist.

This . This may be a nickel allergy. Do you wear anything around your waist that is metal? Even if you don't wear it every day you may still have the rash to prove it. If this is possible, stop wearing the piece of clothing that has metal. Use over the couter Hydrocortisone up to four times a day. If this does not work or not a possible scenario visit your primary care doctor or dermatologist for an evaluation. Good luck.