How To Treat A Severe Rash After Shaving The Bikini Line?

i reciently sahved down there in the past 5 or so days, and i developed a rash in my bikin zone where my legs and my torso meet. and then it went away and its gone a little farther down there, its just like a bad rash almost and i used a older razor. it lost a very thin layer of skin and it kinda itches. How do i deal with the discomfort, Could there be a underlying problem