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?

Tips:
-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
http://ipod.about.com/od/iphone3g/tp/iphone-battery-life.htm

I dont think its the brightness or the apps, i have had mine for 4 months and just had this start 2 days ago, i work for a major cell provider and have been told that when apple comes out with new phones they bug the old ones to get you to upgrade, i thought it was just a farce but now i am starting to think it is true.