Is it possible I'm pregnant?

I have never missed a period, except when i was pregnant before. I had a miscarriage in May, but have had regular periods ever since. My fiance and I have been trying to get pregnant but just haven't been able to. I am now six days late on my period, I feel the same way I did when I first got pregnant before but I've taken four tests and they all say negative. Is it possible I could be pregnant, or is something wrong?