What Causes Itchy, Patchy Rashes On Right Leg?

i have an itchy rash on my right leg only that comes and goes. there are patches on my knees and ankles. a few blotches on my upper inside thigh. all on the right leg only. and only at night. during the day the symptoms disappear and the rash goes away. I do have a few scars from the day before. I saw a doctor and I drew circles around the rash so that the doctor could see where it was coming from. she thought I was bath soap but that is not the case and it is only on the right leg. any idea what it could be?