No disrespect to the OP, but I see a lot of posters willing to just blindly accept that the psychiatric diagnosis was incorrect. What we have is a poster claiming misdiagnosis, without any evidence to support that conclusion (which he would be ill-advised to post here regardless). The clinician likely had some evidence to support the bipolar diagnosis. Certainly psychiatric diagnoses are made in error, and while it's entirely possible the OP doesn't actually have this disorder, it's well-established that people with BPD often perceive themselves to be completely fine. While the gold standard may be evaluation and treatment by a board certified psychiatrist, good luck accomplishing that in many parts of the country, particularly more rural areas. If a psychiatrist is even available, it can frequently take months to get an appointment. PCPs may not be fully trained to diagnose and manage these issues, but the reality is that they're forced to do it every day because there's no one else available.
It may be in vogue here to slam PCPs for making psychiatric diagnoses, and assuming they're usually wrong, but as mentioned in earlier posts, the airman clearly sought evaluation and treatment for something, and didn't like the answer he was given. And he doesn't reveal his age, family history, or symptoms -- nor should he, in a public forum -- but in certain demographics, BPD may not be evident until it suddenly is, often dramatically. It's not inconceivable the OP obtained his ATP and an airline job before becoming seriously symptomatic.
As discussed above by Drs. Chien and Bahn, once the FAA sees a diagnosis in an airman's medical records, whether psychiatric or medical, it assumes the diagnosis to be correct unless and until the airman can prove otherwise. While pilots and wanna-be pilots disagree with this system, can you imagine a scenario in which, given a disqualifying diagnosis, the FAA simply accepts the airman at his word that the trained, experienced clinician was wrong and non medically-trained pilot doesn't actually have the condition? That would be chaotic, to say the least. I hope for the OP's sake he can establish a less onerous diagnosis, but it will undoubtedly be an extensive, expensive fight. And if he does suffer from the diagnosis, his goal needs to be getting on the right meds, and adhering to treatment recommendations. If that's the case, his flying days are unfortunately over.
[Edited to add an additional point, which is that psychiatric diagnoses are often much more nuanced than medical diagnoses. You either have diabetes or you don't; you have a kidney stone, or you don't. There's not much room for disagreement here, yet in psychiatry, I have personally seen, on more than a few occasions, residency-trained, board certified psychiatrists disagree on a diagnosis. For many mental health conditions, there are few objective tests available, and evaluation and diagnosis is necessarily more subjective. A lot of folks outside medicine aren't aware of this, assuming establishing a psychiatric diagnosis to be clear-cut. Obviously, this further complicates determining the eligibility for a medical in the aviation world.]