Iphone 5 battery consumption increased and overheat

Currently I am using iphone 5, ios7. I encounter problem when I switch on my 3G. The consumption of batter increased dramatically recently and caused my phone over heat. I closed all apps, hotspot, Bluetooth. The problem only occur when 3G switch on. When I was charging my phone and playing game, there was no problem. Any experts could advise whether this is an software or hardware problem.... Thanks

Best regards

Alden