Help - Have I been hacked?

Hello everyone. I know that you all will probably say that I am crazy, but I just have to ask these questions. Lately I have the feeling that my iPhone 4s has been hacked. The battery is draining very quickly, even when I am not using my phone. I have tried everything I can think of to make the battery last longer, but it does not seem to work. I always shut down all of the apps when I am done using them. I turned off wifi, bluetooth, location services, etc.
Also, my phone has been randomly sending text messages to people. Some of these messages have been to people I haven't talked to in a very long time so I know that I didn't accidentally send them something or forget that I sent them something.
Overall, everything has been running very slow on my phone. I can barely get safari to load anymore.
I'm just wondering why this is all happening and if by chance I have been hacked. I have reason to believe that a co-worker of mine may have done this. Another question, would he have to have physical possession of my phone in order to hack it, or would he be able to hack it some other way? I used to connect to our wifi network at work and I am wondering if he would be able to hack my phone through the wifi network. He is extremely skilled with computers as he happens to be the IT guy at work.

If anyone knows anything at all about this, please help me.
Thank you so much.

It's very unlikely you've been hacked and even less likely that it's been done over wifi. If physical access was given and the phone was jailbroken then anything is possible but I'd suspect battery failure first.

However, as a place to start I'd suggest connecting to iTunes and doing a full backup - restore - sync.

There are no really security threats right now with the iphone. and as far as i know the 4s still can not be jailbroken if it is on iOS 5.1. Try restoring your phone and seeing if that helps. If that does not work then contact apple and get a new phone under warranty.