It's not uncommon for people to be diagnosed with Borderline Personality Disorder instead of Bipolar Disorder, or vice versa. One of the main differences is that with Borderline Personality Disorder mood changes are often triggered by interpersonal stressors (i.e. conflict or loss) and there is a strong fear of abandonment. Moods in Borderline Personality Disorder can also fluctuate multiple times per day, and there are not always sustained mood states like there are in Bipolar Disorder. It would be important to take stock of some of your history and see what makes more sense. It is possible to have both. It can sometimes be helpful to do a mood log to track your moods and stressors, but it can also be helpful to look at the criteria for each disorder and make a list of any symptoms ore experiences that fall into those categories.

Whatever happens, a diagnosis is only helpful if it informs treatment or gives you a sense of direction in how you want to move forward. One of the main treatments for Borderline Personality Disorder - Dialectical Behavior Therapy (DBT) - can be very effective for a variety of issues. Medications are typically not as effective for the personality disorder piece, but they can still be helpful for some symptoms.

Bottom line, if you have questions, make sure you talk to the provider and ask more about why they believe in this diagnosis. It's also good to continue to educate yourself and make sure to push back if things don't make sense. Good luck!