If your psychiatrist can't tell you for sure, you might want to get a second opinion to get a full evaluation. I suspect that if they "weren't sure" you probably aren't bipolar, because the symptoms are usually pretty clear. Have you ever had times where your mood was really elevated, like you felt like your thoughts were racing and you felt really excited/elated or really angry for no reason? That's mania, and if you've never experienced the manic (or hypomanic) side of bipolar, you probably aren't bipolar.