Bipolar and borderline share a lot of characteristics, and BPD can be very, very, very hard to distinguish from rapid cycling bipolar. Rapid cycling most commonly occurs in women with bipolar II. There is also a higher rate of BPD with bipolar II. That's not to say rapid cycling and BPD never occur in bipolar I —they definitely can and do. BPD with bipolar II, though, is a hard diagnosis to reach. Full blown mania is pretty hard to hide, but hypomania can be elusive and subtle. It doesn't have to last as long either. Hypomania needs to last for at least four days to meet the clinical diagnosis level, which is three days shorter than the requirement for mania (one week).

This probably isn't want you want to hear, but do you have any friends or family members who've perhaps witnessed you hypomanic? A lot of times with bipolar disorder some doctors don't put much stock into what patients say, because we all seemingly lack insight. B********, I know. I personally didn't get a proper diagnosis for years because I'm apparently high-functioning (don't feel like it) and generally do have some insight (the great exception being when severely manic or severely depressed). I was good at faking normal, so they'd look at me like I was nuts if I disclosed any serious symptoms. I've also had some anxiety issues since I was a kid, so they thought perhaps I was just nervous about my symptoms. I could see how they might make the same kind of assumption when they've diagnosed you with BPD...