I use to have this issue too. I would wake up on the middle of the night and itch all over the P. on my legs. I would not have it any itching anywhere else I had P. just my legs. I talked to my Doctor about this and he said the skin on your legs is different than the rest of our bodies. ( more sensitive ) to different enviromnetal conditions. I tried using a laundry detergent that is free of scents and perfumes and it helped alot..I also wash my bedding more than I did before maybe 3 times a week.
You cant imagine how much this has help. I'm till the point if I start to fell itchy its time to wash the sheets. There is alot of thing in your bed sheets I dont want to think about. So try some good detergent and wash your bed sheets often and see if that helps.