I don't put much stock in diagnoses. If they fit with what you can identify with, then it can be comforting to know that someone gets what you're going through. But other than that, mental health diagnoses are subjective without physical proof, so any old schmuck can slap a label on you while the next schmuck says the first schmuck is a schmuck.
I always forget whether BPD is bipolar disorder or borderline personality disorder, but here are my thoughts on both:
Bipolar
If you EVER say a relative (especially parent/sibling) is bipolar, you will without doubt get this diagnosis. My mom has that and schizophrenia and any doctor I've mentioned it to automatically assigns it to me, although I and the others have never had a manic episode in our life. A recent hospitalization for Meagan's suicide attempt and hearing voices that take control of the body...and she was discharged 5 days later with bipolar disorder. What a crock.
Borderline
This one is the diagnosis they give if either 1) they can't figure out WHAT you have but have to put some label (look at the criteria, practically anyone in the world could meet them

) or 2) more commonly, it is a diganosis given to anyone who is considered difficult to work with or a troublemaker. In general, a borderline either adores you or abhors you with a rapid switch between the two. If you are EVER given this diagnosis and are not at least 90% sure it fits, I WOULD NOT repeat it to any other professional because the standing reaction is that borderlines are very challenging and fatiguing to work with and some will just write you off because of it. As a side note, many experts in the field of DID argue that borderline should be grouped with the dissociative disorders and not the personality disorders.
So anyway I agree that you should stay around if this forum is helping in any way. I mean what can it hurt? And when you deal with therapists and doctors, don't waste precious session time trying to adapt to some diagnosis. Just deal with what's REALLY bothering you and get advice on that. Forget about what they think of you, what diagnosis you have, etc, and just tell it like it is. And don't forget to immediately tell them when they are not "getting it" so that the time is not wasted by going the wrong direction. That's the only way to get real help considering the limited resources. Sometimes I make a list. It keeps us on track and I don't go away thinking 'crap I wanted to discuss
yadayada.'
Finally remember that a T sees you way more often and knows you way better than any 5 minute session with a
oooo-big-kahuna doctor
Good luck,
Whats-Left-Of-DeAnna