Hopefully your new therapist will be helpful. If you are questioning the diagnosis, could you ask for another evaluation from the same doctor or a different one? My therapist actually has said she does not see bipolar with me, even though my psychiatrist diagnosed me after observing me for a year, so it's interesting what how different professionals can come to different conclusions. Also, something to consider is that borderline personality disorder and bipolar can co-occur as you might know. I am sorry you experience the low periods, and hope you find treatment that helps you.