My neighbors daughter had something like that during the fall season and it turned out to be a new sun screen lotion that she was using.

I also know of someone that was so alergic to poison ivy that they got it internally via the blood stream.  The rash came out in the most unusual places!(;>).

I am sure that you have tried all the standard anti-itching lotions and it sounds like these are desperate times.  Maybe if you try a topical numbing cream (Emla) it would help calm the itching.  It worked on a bee sting that my daughter got.  She stopped crying almost immediately.  I also used it on a terrible burn I got while cooking stir fry(:o) and it stopped the pain enough to let me function in a normal way and have some good laughs with our company.

If the rash has open areas this might not be the best time to try it.  But perhaps using it on the spots that aren't open would help to quell the scratching enough so that the both of you can get some sleep.  I know what it's like to be sleep deprived-been there, done that!!!

I wish you both the very best of luck finding an answer to this baffling question.

Keep us posted.(:>)