I have a red rash on the back of my leg and it itches really bad?

Leg itch. A natural question would be to ask if you came in contact with Poison Ivy or Poison Oak. In any event, if the rash is not spreading you can try Lotrisone (clotrimazole and betamethasone) creme which is over-the-counter. This should help to clear it up. If the rash is spreading you should probably see a Dermatologist.