A misconception I keep seeing about bipolar is that it's a quick switch in mood from one extreme to another that can happen within a day. And while that can certainly happen if you have bipolar that's not part of the criteria for it. There would have to be evidence of previous (hypo)manic and depressive episodes that have lasted a certain amount of time (and other crap, you can look up the criteria for bipolar on google).

Look at your past history with mood episodes and see what you can find there. I don't sense borderline from your post like another poster mentioned as it doesn't seem like you're being triggered by anything in particular. When did this start happening by the way?