Very possible you are having an allergic reaction? Soap could do it. Metal is a good one. Rough clothing could be a problem.
If your a female and shave, is it the same kind of rash you get when you shave your upper legs then put on jeans?
Try eliminating possible causes:
Laundry detergent
Different clothes
Lotion or soap
Fabric
Belts
All kinds of stuff.
Hope this helped
you could be allergic to metal. are maybe the soap you are using to bath with or wash your clothes in. It is an allergic reaction to something. think of something new you are using. mandy876
If you only get this irritation when you sleep with your clothes on, then it clearly is an allergic reaction to the fabric not allowing your body to breathe.
Take your day clothes off before going to bed and use nightwear or sleep naked.
it could probably be heat rash or irritation from your jeans.