Why do I have this reaction on my left leg when ever I wear the pressure wrap?

I have a pressure wrap for when my sciatic nerve flairs up. It works wonders for me. Instant relief. And if I wear it 24 hours a day for a 2 or 3 days my entire back feels better. I even sleep deeper and better.
Well, recently I wore it on my right leg for two days, then switched to my left leg for 2 days (taking showers in between times) at woke up on the 2nd day with left leg itching like crazy where the wrap was. I ripped it off and scratched and scratched. That was two days ago and now there are long lines that just itch like hell running around on my left leg. It looks like poison ivy or something.
This happened the last time I wore it for an extended period. I even showed the Doc, and she just shrugged.
DO NOT STATE THE OBVIOUS! DO NOT DO IT!
I am curious as to why this happens, and why only on my left leg? It doesn’t happen on my right leg. I’d ask our resident Doc but he’d just shrug and say, “Shit happens.” :D