You could download all the AVG new versions and the upodates for a year and still get nowhere near 5GB..:-)
Perhaps someone else is using your system?
Easiest way to keep an accurate check on a daily and/or monthly basis is by using Tautology Bandwidth Meter (does as it says on the tin):
Accessing the router will be, most likely, by keying in:
into your browser window and then entering admin (or perhaps Admin) as both the Username and Password into the router's log on panel.
However it just might be slightly different in the case of the Voyager.