Pregnancy: Prenatal Screenings
You are not crazy at all. I had my first child at your age and refused even an ultrasound because I knew that I was very low risk and healthy. I was a fully trained obstetrician by then! I also knew firsthand how distressing false positive tests can be.
In general, our culture goes overboard with testing because our culture believes that more tests will somehow "save" us. Obviously, there is a place for prenatal testing. But it sounds to me as though your inner guidance is speaking to you loud and clear.
Here are the questions you need to ask yourself honestly: "Do I trust myself enough to forgo prenatal testing? Am I willing to accept responsibility for myself and my own decisions without blaming my health care providers if anything goes wrong?" If the answer to those questions is an unqualified yes, then you have your answer.