You sound kind of like how I am when I'm not in an episode. When I'm not majorly depressed or manic, I experience mild, rapid mood swings. I've been told that I have a "cyclothymic temperament" in addition to my bp 1, so maybe you have that kind of temperament too?

If your symptoms aren't bothering you, then don't worry about it. If, however, they're making you miserable then try to find out what is beneath them. Maybe try both mood stabilizing medication and DBT?

Here is an article on the differences between bipolar and BPD: borderline