People are not born with a personality disorder. They are maybe born with a certain temperament, the rest is a result of psycho/social influences. And I'm sure there are a lot of people out there with a personality disorder that not have been diagnosed.
Your question where your emotional inhibition comes from, I can't answer that. In my family we are very inhibited and we don't talk about emotions at all. While with the rest of the world I am open to both talk and show my emotions. I understand that you want to know where your schemas come from, so do I and I am still figuring out. More important however is that you recognize your schemas, you already do, and to develop more appropriate coping mechanisms and a good therapist should be able to help you with that.