physical sensations when using iphone

Recently I have noticed that when I hold my iPhone with my left hand, I experience a burning sensation on the skin of my left thumb (It feels like scalding). It is not the joints, only on the skin. If I hold the phone for any length of time, then move my hand away from the phone, it continues to feel like my skin on my thumb is being scalded if my hand is even close to the phone. But, when I move away from the phone, or put it behind my back it stops. It only happens when I am either using the phone, or if my hand is near the phone. I wonder if it has anything to do with radiation?

At first I thought I may have scalded my thumb, so I waited about a week. However, the feeling continued. It has been about 2 weeks now. It happens every time I use the phone, only happens when I hold the phone. Only on my left thumb.

If I hold the phone with thick cloth between my thumb and the phone, it doesn't hurt. It happens every time I use the phone for about 5 mins or more.

Has anyone else ever experienced this?