What uses up my data?

[<3]

I have the iphone4 and i try to use wi-fi as much as possible. I always try to use the internet and games when there is wifi, but recently my usage went from 62/300 to 158/300 within a day!
I had games like metal storm, words with friends and draw something but i deleted because i thought it was the reason why.

i had city story but it pissed me of so yeah oh and ninja fishing

sometimes my wifi at homes disconnects when i don't realize but i always check so it reconnects.

i use tango and facetime alot too..and i have a twitter app..

So any ideas why it used so much and how i can stop from using so much?
thankkks