Go to the doctor asap if uve had a tubal litagation you can fall pregnant but the pregnancy will not evolve into a viable pregnancy. Its called an etopic pregnancy or a tubal pregnancy and is very dangerous. If you are indeed pregnant there ia no way to save the baby as it is stuck in the fallopian tube. Good luck.
I would take one more test. I saw a post by a doctor on this forum that said a tubal ligation actually cuts the tubes (doesn't "tie" them) so they cannot "grow back together."