You can review your iTunes Store account purchase history at any time to see what items have been ordered using your account. The following article will walk you through the steps:
Seeing your iTunes Store purchase history and order numbers
http://support.apple.com/kb/HT2727
If you are unable to determine the source of these charges and find that they are fraudulent, I strongly recommend you change your account password and security question immediately. Changing the password and security question will help to prevent anyone else from using your iTunes Store account to place orders without your knowledge. To increase the security of your account, choose a password that has at least eight digits and includes both letters and numbers. You can change your password using this website: