iPod Touch 5th Generation, Battery loses charge too quickly!

Hello All!

I've been using iPod Touch 5th Generation for 3 months now, but now, all of a sudden, it loses it's charge extremely quick, it used to hold for 2 to 3 days, but now, it drains itself without doing nothing! it even loses charge while turned off ! (well, hybernated or whatever) I reseted it, charge it completely, 100%, and now is almost at 20% without doing nothing!

It has iOS 7, but no update yet,

Any advice is greatly appreciated,