I read many many books, re-read my personal journals, and basically had self-diagnosed by the time I spoke with a psychiatrist, who agreed with my assessment upon presenting the evidence.

The huge challenge with diagnosing type 2 BPD is that it basically needs a historical time series of data to be detected properly, so either you or someone close to you needs that data. It's believed to be a lot more prevalent in the population than officially diagnosed, which sucks because it results in consistent, increasing depressions that don't respond to treatments for "unipolar" depression (major depressive disorder), which are actually dangerous as they can trigger mania.

I was lucky that the first medication I found worked really well with no side effects, and I basically went from "random 3-6 month depressions every 1-2 years" to "normal person", which removed a huge debuff, in video game terms.