Based on the information provided its nearly impossible to tell whether or not WordPress is the cause of your problem. However its almost certain that its not.
That amount of bandwidth is highly excessive for it to be contained to a "problem* caused by the WordPress core itself.
You could attempt to inspect the amount of database queries being conducted per-transaction/request but in saying so you should also see some sort of correlation between increased database usage and your site traffic.
In fact inspecting your traffic logs will give you an indication if there has been a spike in traffic and if so, where that increasing traffic is going to (what page/location) within your site structure which may include accessing files directly and not necessarily anything within your WordPress page structure.
I would question your hosting support about this matter as they have the proper tools to analyze this problem.