How do you know if you're "addicted" to Vicodin?

I have been taking it for about 2 weeks for a series of reasons. I ONLY take it when i'm in physical pain. However, I find that when I take a vicodin, i'm much more chill & relaxed & when i'm not, i'm a little less patient & irritable. Is this the begennings of dependency or just the vicodin doing what it does?