IPhone battery dies quickly?

I have an iPhone 4S and this week it's been draining more than ever. I haven't been using it anymore than I usually do. When I get home from schools it's at like 10 percent which it's usually just at 60. Even when I put my phone alway and use it like 3 times the whole day it still does so quickly. 15 minutes after I charge it it's at 70 percent. I try closing out my apps fully and turning my brightness on all the way low and if still hasn't helped. What's wrong with my phone and what should I do?

-turn on autobrigthness/reduce brightness
-turn off bluetooth/3G/4G/wi-fi off when not needed
-turn off location services and data push
-fetch email less often and autolock faster
-turn off equilizer