IPhone :: How To Retrieve Lost Data From It

first off, something strange happened Nov 20, 2011 because that is the day my voicemail stopped working. ATT and APPLE could not figure out how to solve the problem - so I just had no voicemail until yesterday.

My iphone 4s' volume button broke, so I took it into the APPLE store to get a new phone. I backed up before I took the phone in, because I was pretty sure they would replace my phone - which they did

When I restored the phone to the 'most recent' back up, I lost ALL the data on my phone after Nov 20, 2011. All my texts, all the data about my baby that I have been keeping in a baby app - basically any app info. Even my camera roll reverted back to the way it was on Nov 20. (fortunately I had saved my pics to iphoto - so nothing really lost there)

I don't understand where all the info went when I backed up RIGHT before I went to the apple store.

I have looked on my computer and found the back up file, but I don't know what to do with the info in there. Oddly, I can't find a back up for 4/2/12 - the day I did the back up, but there are several back ups in March.. which would be better than the NOV back up.

Info:
iPhone 4S, iOS 5.1