It's only been a week and att says I've use up 90% of my data(iPhone 4)?

I check my mail often if I have any mail even when I don't have Wi-Fi but that hasn't effected my data in that past. Other than that I use Wi-Fi and don't ever use the 3G(unless the mail counts).

Um… Okay. It's hard to help you without knowing your data cap. 90% is just an arbitrary number. 90% of 100 MB is 90 MB, which isn't much. But 90% of 1 GB is 900 MB which is a lot more usage than the previous example. If you have a very small data cap (like 100 MB), it wouldn't take you long to reach that cap. Are you absolutely positive you're not streaming any data (like Spotify, Pandora, YouTube, etc.)? Even just browsing Facebook can consume multiple megabytes every few minutes.