My iPhone 4 keeps restarting by itself. How can I fix this, what is casusing it?

I've seen several other adds about people saying their iPhone automatically resetting as well, but no salutions or advice of why it could be doing this.

My battery seems to drain pretty quickly now too. 100% to 20 In maybe 20mins.

My phone gets really hot randomly from it also.

What causes it? How can I fix it? Will apple replace it?

It can't be an app, I havent made changes to my phone in months, and yes. It's on the most recent program for the iPhone.

Ill add the reset occurs when making attempt to edit pictures in the regular album. Never had a problem with this before tonight.