This isn't very scientific but I like to think of it this way:-
Mood swings are like waves, with the peaks being high points and the troughs being the low points. The wavelength is the period between mood changes.
Everyone on the planet is on that continuum somewhere, so, if you like everyone is bipolar to a greater or lesser degree. What matters is the extent to which it impacts on your life. If it doesn't cause you problems, then it doesn't need to be given a label.
People with smaller peaks and troughs, we tend to call cyclothymic. If the peaks and troughs are bigger we call them bipolar.
Some people like to have labels they can attach to their illness. As long as they're coping I'm not sure it really matters.
Do your mood swings cause a problem for you? Are you on any treatment or medication?
Take care
There is a form of manic-depression that is called 'rapid cycling'.
This is quick moods between mania and depression. see:
http://bipolar.about.com/cs/faqs/f/faq_rapidcycle.htm