NotReady's My Pregnancy Wish

I hope that I am not pregnant, I'm not ready to be a mom. Every pregnancy test says negative, but I have not had a period in 153 days. I am overweight and concerned that it could be concealing a baby bump. I never felt ill in what would have been my first trimester, but now I'm afraid that every lower ab muscle flutter is quickening. Why can't I believe the tests and get on with my life?