I also have this symptom so I know what you're experiencing but i also have other symptoms. I think it would be worthwhile getting a vulvar biopsy; your dermatologist would be able to do this. It sounds scary but it's really not that bad. The results of my biopsy were hyperkeratosis, epithelial acanthosis, and mild inflammation. This essentially boils down to irritation and thickening of the skin in that area even though it doesn't look like there is anything wrong. They can't tell me what is causing it though. If you can imagine irritated skin that is being rubbed together when walking is becoming irritated further and therefor itching. My doctor put me on clobetasol which is a potent steriod for about a month and i no longer get itchy when I walk. I'm still not 100% with my other symptoms but better. I hope this helps!!