A few weeks ago I started having a strange sensation in my right thigh. When I moved my leg, it felt as if something was slithering between my skin and my muscle in the marked area (these are not my legs, just a convenient image I found on the internet)

Mystery solved. Whenever I had been sitting down with the key in my pocket it had pressed up against the area in my pelvis that the nerve passes through. Sure enough one week after no longer carrying the key there, the problem has completely disappeared.

Leaving just one question: where to carry the key instead?