Hmm, well first thing I suggest you do is download Spybot S&D. Here: http://spybot-download.net/
Update it, unplug your net connection and run it under admin privileges. Been using it for years, picks up a lot of stuff some main line AVs don't.
Next make sure your dont have any file sharing/torrent clients running full time. If you are seeding a ton of things it could whore you usage.
Also, check your processes that are being ran under task manager to see if any one program is acting up.