Christina,
You could be a 'rapid' cycler, but you can also be 'bipolar II" which is a lot milder than 'Bipolar I'. But you do not want to ahead of the doctor and self-diagnose yourself.
I have a lot of mixed-states (Bipolar I), and from what you describe of your symptoms being a few days. I would have to say it might be something else. My mixed-states last longer than a week, probably more like a few weeks. It is usually a state of mania and depression all mixed up in the mix.
Rapid cycling, is if you have your symptoms 4+ times a year. A few good days, ending in a crash that is a few days long too. This is the hardest form of bipolar to treat.
Bipolar II/Hypomania is when symptoms are milder than Bipolar I, but should not be ignored none the less. It usually lasts less than a week of hypomania and can follow/or not have another week of so of depression.
I hope you the best on your diagnosis. Please do not feel too discouraged, and know we are here for you when you need to talk.