Tracking broadband usage

[#1]

Hi there,
As a light browser, my broadband usage for the past 3 months has been around 800-900MB, but this month I have already reached 1.6GB - with still 12 days to the end of my month!
Today, for example, I used a total of 180MB - yet have only checked emails (downloaded 3 without attachments), browsed a few websites (nothing with video etc) and run a virus scan. And there haven't been any Windows updates since the 9th.
Can anyone tell me if there's a way of tracking which programmes are accessing the internet and how much they are using? I'm just concerned that (despite having up-to-date anti-virus/malware) there may be something using my bandwidth that I don't know about!
Also just to note that I've checked and no other devices are logged onto my wifi (and yes, I have changed the WPA codes from the default!)
Any help / reassurance much appreciated,
Thanks,
Stuart

[#2]

For tracking total usage I've recently switched to http://www.softperfect.com/products/networx/
If you have multiple PCs it will give you the total and it's intelligent enough to ignore the local network traffic which is a failing of other utilities.