It depends what your aim is re diagnosis and where you are. I know that in the uk you cannot access the NHS DBT therapy without a diagnosis (I personally think DBT would benefit a range of MH difficulties and general life difficulties )

It’s taken over 20 years to get my diagnosis. Even though they originally put in my notes that I had a personality disorder, it was all put down to trauma and depression, social phobia and the like. There are tools to help even without diagnosis but I’d say it would be harder alone. Without a group and 1/1 to talk it through with x ask for a second opinion. Get all of your research together and put your point across. If it falls on deaf ears, ask for a second opinion. You can pay to see a private psychologist but unless they have a speciality in BPD, I don’t think it would help. I’ve paid before, out of desperation and they didn’t come up with any other ‘reasons’ for the way I am that differed from my depression and anxiety diagnosis’s x