Hi!
When I was pregnant with my 5 year old daughter, my test came back positive twice, and I had to have an amnio. I was 21 at the time, and had had two healthy boys before (they are 9 and 7 now), so I was worried just like you. The procedure itself was fairly painless. It's like going in for an ultrasound. The technician finds the baby on the screen, then looks around it for the greatest concentration of fluid. The needle is inserted while the doctor watches on the screen. After the fluid is extracted, you may feel a liitle sore in the area, but it goes away after a few hours.
Thankfully, the test proved to be negative for d.S. And/or any serious birth defects. However, I wound up having my daughter two months early because she had a block in her intestines which wasn't allowing her to digest properly while in the womb. What really struck me as "funny" was that I had had an ultrasound two weeks prior to going into preterm labor, and the doctors did not see it, but when I was admitted into the hospital in another state for her birth, they picked it up rather quickly. She had corrective surgery eight hours after she was born, stayed in the hospital for two weeks, and has been a happy healthy, beautiful child since. I believe that it was the blockage that caused the positive result for my two tests.
My advice is for you to have the amnio, and if (and prayfully when) it comes back negative, get another ultrasound and have them really look at your baby. Good luck and god bless!!