Audacity changes Sound Settings

I find that when I use Audacity, it changes my sound settings. It will change it so that when I listen to stereo files that I can only hear it in one ear. Plus this continues when I later listen to things on my computer (iTunes, YouTube, etc.). How do I fix this?

Thanks!

What sound card are you using?
Where are your headphones plugged in, and how are they connected?
If you are recording, what are you recording and what equipment are you using?
Why do you think that it is Audacity doing this?