Hello! What you're describing certainly sounds like BPD or something similar. Of course the only way to find out if you have BPD or another personality disorder is go to a psychologist or psychiatrist for a test (please don't settle with your pdoc for this, BPD is still very stigmatized and pdocs generally just aren't competent enough when it comes to mental illness), but I can think of a few questions that might help you understand what label you fit into (because there's obviously something there, even if it's "just" recurrent or chronic depression, dysthymia or addiction - I have BPD, bipolar with a very chronic depression, substance abuse and I used to be addicted to computer games, so I think I should know). Also remember that the diagnosis you get isn't the best description of your problems - that would be the individual traits you have and how they are spread across the spectrum of personality disorders.

Ultra Darkness's question is very relevant. How do you feel when you sense that people are rejecting you, or even worse abandoning you? How do you react to a real or imagined sense of rejection or abandonment? Most BPD patients that I have met have serious issues with this. However, as I said, it's the number of traits that matter, not so much which ones, and you might be atypical or not meet the diagnostic criteria but still need treatment for BPD.

Are you impulsive? Self harm is usually impulsive, and if you've abused drugs that could be impulsive too. Are you impulsive in other ways? How are your real-life friendships, if you have any, and other human relationships? Are they stable or chaotic? My relationships are very stable now and I generally don't do impulsive things anymore, unless I'm hypomanic. I still score very high on tests for BPD.

You say you mostly keep inside and to yourself because of anxiety, but do you miss being with other people? If you don't, I would be quite certain that you do not have BPD. Suppose your anxiety was gone, would you then want to spend something like a normal amount of time with other people?

Do you often feel empty inside? Do you feel you don't know who you are, or maybe you don't even care about who you are? Do you often act like a different person around different people? These are very common problems.

How do you think your levels of emotion are compared to that of other people? Mood swings are common in BPD, but often they can be better explained as something else, especially if they lack a clear cause. However, fluctuations in feelings (as opposed to moods) are one of the main symptoms of BPD. This is lability - you will often find yourself reacting to something with an emotion that is out of proportion to what actually happens. You might not realize that the reaction is extreme, because you are responding to a very real perception and strong feelings cloud ones judgement, but maybe other people have often told you that your reaction is inappropriate.

How do you respond to emotional stress? Do you sometimes find yourself unable to think clearly because you simply feel too much of something - anger, resentment, sadness, joy, anything? Maybe you can't think at all? If this happens as a spontaneous reaction to something, and not as a mood or something that just pops up without any cause, it's indicative of BPD. Also, do you often get angry? Does your anger seem stronger or seem to last longer than when other people get angry? Repressed anger? This can be a symptom of many disorders, but also very much of BPD.

I wish you good luck!