Hi,
This could be due to an allergic rash.Any change in bed-linen or some new clothing maybe?
Try an OTC anti-histamine and apply calamine lotion.
Contact dermatitis is the name for any skin inflammation that occurs when the skin's surface comes in contact with a substance originating outside the body. There are two kinds of contact dermatitis, irritant and allergic.
Or it could be Irritant contact dermatitis (ICD), the more commonly reported of the two kinds of contact dermatitis, and is seen in about 80% of cases. It can be caused by soaps, detergents, solvents, adhesives, fiberglass, and other substances that are able to directly injure the skin.
The best treatment for contact dermatitis is to identify the allergen or irritating substance and avoid further contact with it.
ref:http://www.myonlinewellness.com/topic/topic100586656
Any more clarification will require a visit to the dermatologist.