I just really need someone's input on this.?

I think I might have borderline personality disorder. Or at least something similar to it. I took 3 different online test for it and they all recommended I ask a doctor about it. Then I talked to my psychology teacher about it and he told me I should see a doctor as soon as I can. Normally I would have ignored it and assumed it's just anxiety but I think I might actually have something. I love helping people but anytime I feel like I'm not helping someone, even a little bit, I get depressed and often even suicidal. I've made a few attempts but in the past I always knew I had someone who needed me around, whether it was a girlfriend, my cat, or just a very close friend and this always stopped me from following through. Now I often feel like I don't have anyone who needs me anymore and it makes me feel completely worthless. I find that the worse of a mood I'm in the more reckless I become. When I mess something up and get irritated sometimes I literally beat myself (slapping, punching, kicking, etc.). When I think I'm losing someone close to me, even if it's obvious that I'm really not, I do everything in my power to avoid it. Sometimes this actually leads to me driving people away. I have a few friends who always come to me to talk about their problems, which brings me a lot of joy, but I never feel I can share my problems with them and I feel terrible about it. They can usually tell when something is wrong and they try to help me but every time I turn them down.