[Batman.]

Well somehow I doubt you'll know from an online test, or your doctor.

As said, Borderline Personality Disorder isn't usually diagnosed until the patient is 18 or older (nor is any other personality disorder, really) because your personality is still developing in your childhood and teen years.

Your family doctor (aka your "GP" [General Practitioner]) cannot diagnose personality disorders. GPs don't have the proper training to diagnose personality disorders, most mood disorders, or many other mental health issues (except Depression and Anxiety, since the symptoms are pretty cut-and-dry). If they were able to, they'd be psychiatrists. Point is, you HAVE to see a mental health professional for mental health issues, which would usually be a psychiatrist. Mental health professionals are the only ones qualified enough to diagnose things like Borderline Personality Disorder, Bipolar Disorder, Schizophrenia, and anything else you can think of. Your GP, however, is not qualified.

Third, looking at a list of symptoms, and taking online tests, aren't diagnostic tools. Not even close. If you're worried about your mental health, and/or are causing harm to yourself, you should probably mention this to your doctor (GP). They would need to be involved in the process of being referred to a psychiatrist, if there is need for that (which, for things like Depression and Anxiety, there usually isn't a need to be sent off to be diagnosed).

Hope this helps.