Could it be Borderline Personality Disorder, am I too young to have it?

It's a common misconception that you have to reach a certain age before you can develop a personality disorder, but they are coded on Axis 2 of the DSM because they are long-lasting, chronic, difficult to treat problems. You may have a hard time being diagnosed with BPD (because of your age), but you don't have to be a certain age to have BPD. From what you said, it sounds like you fit a lot of the diagnostic criteria for BPD. I would definitely bring it up to your therapist and ask him/her if they can recommend someone who knows Dialetical Behavior Therapy. It's a new treatment developed to treat BPD and it shows some very promising signs of being successful. You do not have to life this way, there are people who want to help you be the best you you can be. Hope this helps.