400mb data used in 2 days on iPhone 4

Ok so I use to have a blackberry on my old sim, I had 100mb and used Facebook+Internet and BBM and stuff everyday an in a month that uses about 60mb, but now I've got an iPhone 4 I got a new sim with 500mb and I've used 400mb data in 2 Days! I use Facebook, YouTube, Instagram, Internet, games that use data. So what's wrong? Why's it eating up all my mb's?

Open up your phone & look. All of the information is there.

The reason could be that you're heavily using those apps.

Youtube is the main problem… You will get a big amount of data left when you don't use youtube