I have a better grasp of the first part of that question than I do of the second part.
I developed, "got", began exhibiting symptoms of, or was diagnosed with Obsessive Compulsive Disorder when I was 27 yrs. old after the birth of my son. But the seeds of OCD were sown much earlier than that -- when I was in the womb.
As I understand it, the source of this disorder lies in the coming together of three different aspects of my life. The first is genetics. I was born genetically "pre-disposed" to developing OCD. It is as if my brain was created with a special garden in its make-up that has fertile soil that was just waiting for the seeds of OCD to be planted.
The second "prong" of the OCD trifecta is environment, or the events of my life that produced the "seeds" of OCD that landed in the fertile soil in my brain. Is this garden metaphor still holding for you? An example of one seed would be my birth order. I am the oldest of three daughters in my family. The way that I interact with the world around me was determined in my childhood by the way I interacted with my siblings and my parents. I was a classic over-achiever who was always trying to impress my parents. Other "seeds" planted in my early years might be the kind of parenting that I received, the values of the community in which I was raised, and significant events in my early years that would have reinforced my need for control.
The third prong is a traumatic or dramatic event in my life. This prong would be the "trigger" that brings on the full blown Obsessive Compulsive Disorder. Most women who are pre-disposed to OCD develop it in their late twenties. So it is no surprise that many women develop OCD after the birth of a child.
So I had the potential to develop OCD because of my genetic make-up, but it was the combination of the circumstances of my childhood and teen years, and the birth of my child that brought on the actual "disorder".
Before my son was born, I was an anxious person, but I did not suffer from OCD. After I went through the ordeal of labor and delivery, I found myself struggling with obsessive thoughts and the compulsion to wash and re-wash my hands -- thoughts and behaviors that I did NOT have before that time. I read a theory that women who develop OCD after childbirth produce an over-abundance of the hormone oxytocin (pitocin is a drug form of oxytocin that doctors give mothers to induce labor). I don't know if this is true, but I do know that I came out the other side of childbirth with my brain totally re-wired -- and not in a good way.