99% data usage in 24 hours of new billing cycle?

So last month I received the "You have used 65% of your 2GB data plan allowance for the bill cycle ending on 04/26/13." Which was odd because I had received it pretty early in the month, on the 10th. My data usage involves maybe 10-20 minutes a day on data which is just quick scrolling through facebook, instagram, and twitter. The rest of the time I'm on Wi-Fi. I've been doing that since I first got my phone (Iphone 4S, running through AT&T) and I've never received a text like that before. Well, I began to use my phone more scarcely; tiptoeing around, only using data when i "needed to" and all was well. Never got a 90% text message from them.
Yesterday was 4/26/13, the last day of last month's billing cycle. So I felt a little freed so I used a little more data. Yesterday I believe I used probably about 25 minutes on facebook, instagram, tumblr, and twitter. The rest of the day was spent on Wi-Fi. Well I go home, sleep, and wake up this morning- the first day of the new monthly billing cycle and receive this text: "You have used 90% of your 2GB data plan allowance for the bill cycle ending on 05/26/13." How could this be? I can't check online because my cousins pay for my phone, not my parents. This is also another reason I really don't want to go over. But I don't know if I can go an entire month without checking things, etc.
My cellular data usage doesn't reset automatically in my phone and it says "Sent: 565 MB Received: 5.2 GB" and I know that yesterday it said 5.1 GB. I've had this phone since November. Also, I thought it might be wise to call the *DATA# number to get the text message stating just how much data I've used or whatever, and I received a text message from AT&T saying "We're sorry. Requested information is currently unavailable. Please try again later." I don't know what to do. Please help!

Added (1). Well yes, but ever since 9:30 pm last night I've had my data completely turned off.

Do you have an app running in the background? Otherwise you need to check and see how much you have used, if someone else is pyaing then ask them to check for you.