Red Marks On Skin After Scratching, Itching, Feels Warm From Inside

im 29 years old. i usually get this red marks on my skin, it comes in which ever position i scratch and can see the marks red in that way and it itches v badly, n i feel it very warm from inside but it is not warm to touch. Just wanted to know what it might be, coz usually it happens when am at home, n by the time i want to show to a derm its perfectly fine, so dono wot to describe it as. Description: Red rash comes along whereever scratched in the same line, like if i scratch with 3 fingers, u can see three finger lines of red rash...which is itchy and feels warm from inside.