If these rashes are allergic in nature then they would be itchy as you have described and there would also be swelling if you traumatize the area. Most commonly this arises from allergic reaction
to undergarments or clothing as also from food. You might be sensitive to elastic in the undergarments or to specific dyes used in clothes or to foreign proteins
in food. You should resort to an antihistaminic to reduce the itching sensation and apply calamine
lotion over the rashes to get a soothing effect till these disappear. Also, try to identify to what you are allergic to.