my iphone is still gobbling up my alotted data plan since I updated to IOS6. I have an iphone 4 and in the week since I updated it's used more than twice what I normally use in an entire month. Any ideas what the problem might be?

I have an iphone 4 and I finally updated to IOS6 a week or so ago. Ever since then I've gone through my data plan, plus to extra GB's and being charged extra, in just 1 week. I've never gone over my data plan before. I don't have a lot of apps. I always close my background stuff. I'm connected to wi-fi most of the time and rarely use my phone outside of my wi-fi zones. I talked to Apple rep who was nice, but all suggestions failed to help. Any help would be appreciated. Thank you!