Speaking for myself, tests help for about 30 second and then I begin to assume that they missed something. For example, two years ago I had a full cardiac workup (Holter monitor, stress test, and echocardiogram), all of which came back showing a strong, healthy heart. I was reassured for a few months. But the further away from the test you get, the less you believe the results, and start to wonder if something's changed.
Transvaginal ultrasounds are no fun. They basically take a plastic wand thing, insert it, and move it around to get the pictures they need.
Ultimately, a doctor most likely won't give you a test without a documented medical need. And that's good, because you will a) get in the habit of asking for tests to calm your mind and b) that will get prohibitively expensive, especially if you don't have insurance. I racked up $6500 in one ER visit that turned out to be nothing (and that didn't include the $780 from the cardiologists' later that month).