I Have A Red Rash Pattern On The Left Side

I have a red rash pattern on the left side (outer) vagina lip. Seen a dr today and she couldnt explain it since there was no discharge, smell, scabs or anything. it is just a patch about as long as a pinky finger on the whole left side of my outer vagina. It Itches like crazy and even with prescribed medication its not helping. What could it be?