Access your resource monitor. Easy way of doing that is opening task manager, and clicking the performance tab. There will be a button there.
Now, go fire up battlefield. Mid game, alt tab out, and check the total network activity for battlefield 3. It'll give you that in Bytes/sec, so multiply by 3600 (60 seconds/minute * 60 minutes/hour) to find Bytes per hour. Likely, this number is going to be huge. If you divide by 1073741824, you'll get GB/hour. That should give you the best idea as to how much you're using.
Do this a few times to find an average.
Also, maybe read a book or something. 6+ hours a day is a lot 😉