Why is my data being used so fast? (iphone 5 AT&T)?

Before when i had JUST got my iphone 3gs i was going through data very fast but it was because it was my first smart phone and there WAS so much new stuff for me to play with so my mom upgraded my data allowance and i had never gone over since ( i had the 3gs for a good 2 1/2 years) but i recently got an iphone 5 ( its almost a year old) and at first i wasn't going over but now i go over EVERY freaking month always right at the end of the month but now i just got an text saying i've used 65% of my data and its only the 12th! I swear to god i'm not even on my phone all that much besides briefly checking my email or instagram/tumblr/vine i face time OCCASIONALLY like i seriously can count on one hand how many times i've facetimed could there be something else going on? I'm So annoyed!

Added (1). Also we've had AT&T for YEARS (like 6 plus years) and i remember having unlimited data all my friends were grandfathered in and got to keep there unlimited data plan by my mom and i never were? Can we still get that?

Added (2). I do call long distance a lot from WA to CA but i have long distance calling on my plan? If that helps?

so the fletching thing didn't work it was already on manual.

You're likely fetching mail in the background. Go to Settings>Mail, Contacts, Calendar>(account)>and find your "fetch" setting and set it to "Manually." That way, it only fetches when you open the mail app. I did it and it saved me TONS of data. Also consider getting DataMan Next from the app store, which lets you monitor data usage; or, if you're on AT&T, get the myATT app to track usage even better. Also, in iOS 7 you can select which apps are allowed to use data. DEFINITELY enable that feature when iOS 7 GM is rolled to the public sometime later this year!