iphone 4s really hot down camera side

I bought an iphone 4s 16GB four days ago and i have noticed that down the camera side it is really hot just now. i have just put it on charge but i know the battery is on the other side. i have turned everything off like wifi and locations and siri and closed all apps that could be running but it is still hot. i was using it on the internet and apps such as facebook right before i noticed this.
Does anyone know what could be happening?
I dont have insurance on my phone and can not afford a big bill but if there is an issue would i be guaranteed? i live in england and purched the phone sim free from carephone warehouse