Sometimes bipolar is overdiagnosed. It's fine for your therapist to talk to your pdoc so they can coordinate care. Bipolar II can be hard to tell apart from major depressive order if your therapist never sees you during a hypomanic episode. I've questioned my diagnosis before but it really doesn't matter. Your therapist needs to support you and the diagnosis is only useful for treatment. Just let them know you're comfortable with your pdoc and what your goals are for therapy. They should work with you. It really is more of a medical diagnosis and though a therapist can diagnose bipolar it's better for a psychiatrist to confirm it.