Well, I know it's not because you hold the yarn in your right hand. So long as you're purling correctly, doing the yarn over correctly, and knitting correctly, it should all work out. So I'm kinda stumped.
Have you double checked your technique by watching Amy's videos?
How many rows are you knitting before you decide you're doing it wrong? I would suggest knitting an entire pattern repeat first. Maybe it IS right after all!