I relate to all of this. It's so hard to know what's going on.

Atypical depression has features of interpersonal sensitivity & mood reactivity. & borderline PD has similar, interpersonal sensitivity & mood instability that is very rapid & frequently changing but also has other symptoms. Then there's lots of anecdotal stories of this kind of mood instability in bipolar, I think it's called ultradian where mood changes over the day, then there's ultra rapid cycling which is more like days to weeks, then there's just rapid cycling which is 4 or more episodes in a year. Not sure that it's an actual classifier though.