I started out going to my family physician, but most likely they won't be able to give you a definite diagnosis. You need to be observed by a professional in the psychiatric field before you can get a diagnosis of BPD, but it's fairly common and if you feel like it fits you, you probably have it.

I was officially diagnosed only after going through partial hospitalization once, and then inpatient treatment and a second partial hospitalization. My family is still trying to pay off all the debt we acquired from my most recent mental break down. :/ Good luck to you and hope to see you around the forums.