It can take some time and 2 sessions in my opinion isn't enough. Is there family history of mood disorders? BPD tends to be more reactive to life situations where BP can be a mood for no reason at all i.e. I can have things in my life going well, but be depressed for no reason.

I would suggest starting to track your mood and let your Psychiatrist know. I use this online one:

http://www.medhelp.org/land/mood-tracker