Why is my iphone using so much data lately?

I have a 2GB data plan and I've had an iphone for probably 2 or 3 years. For the past year I'll get close to my data limit most months and even go over maybe every 3rd month. With it being every 3rd month (roughly), it was cheaper to just go over and pay the extra $10 than to upgrade my plan. This current billing cycle I hit 60% of my plan in TWO DAYS! I hit 100% after five days. I'm not doing anything differently this month than I have every other month. I called AT&T and they have no idea either. They gave me a $30 credit to pay for my overage fees this month, but that's it. They can't tell me which apps are using up all the data. What could have possibly changed this month? Where is my data going? Any thoughts?

Remove all recently installed apps and then install every day one back and check if data usage is becoming high again. Or maybe you watch to much youtube videos.

Because of the software increasing data, use of memory