It's from all the hits on your sig from this forum
Have a look at your web stats, that'll tell you where the bandwidth is going. It's likely to be one of three things
- You are getting a lot more visitors.
- You're being hit by aggressive bots
- You've uploaded some large file size images that consume a lot of bandwidth when downloaded.
The first one is the one you want, the second one can be good or bad depending on which bots are visiting, and the last one is bad and means you will have to optimise some of your images, Either way, if you check your web stats, the answer will be there.