You will be asked why you left your previous position in your job interview. Just get ready for it. Your future employer will want to know why you weren't happy there (because maybe it means you won't be happy with them, either). Or maybe you'll even tell them something bad about yourself. Stranger things have happened.
So how do you answer? It's not really a matter of telling the truth or not. It's about telling the truth that puts the most positive spin on your situation.
Watch the video and I'll tell you how to answer the interview question "Why did you leave your last position?"
Go to my blog post that explains this in more detail: How to Answer Interview Questions Q89