Iphone 6 overheated, cooled, heated back up.

Hello,

I have an iPhone 6 and I've been using it as usual all day. I was sitting with it in my pocket and when I took it out it was so hot it hurt to touch and it was off. I took it out of it's case and let it cool which took almost an hour. It still wouldn't turn on. Then I left it and waited a bit before trying again but it had somehow heated back up. I waited for it to cool again and then I plugged it in to charge but it still wouldn't turn on and my computer wasn't recognizing that it's plugged in. I waited a while to let it sit on the charger but after more than an hour it still won't turn on but it's not hot anymore. This has never happened before and nothing unusual happen with it today.

Any suggestions?

Other info:

Got my iPhone in this past December

This is my cover http://www.urbanarmorgear.com/products/rogue-folio-iphone-6-plus

That happened at noon today and the last time I tried to turn it on was at 5pm

There is no previous damage to the phone in anyway