Blood Clots!!!

I had my open rny on Oct 15, 2003. Within the past month I have gone through several tests to rule out blood clots. I have had a ct scan, chest x-ray, a nuclear scan, venus doplar, and a D-Dimer blood test. All the tests came back negitive, except for the D-Dimer. The D-Dimer is supposed to show if you have or had a blood clot, unless I am mis-understanding. I am very concerned that the doctors could have missed something. If anyone else is dealing with the same issues....could you let me know. This situation is very scarey to me, and maybe someone could help ease my anxiety about it. Thanks.