A friend of mine experienced the same! She told her periods were always regular even after the tubal. So when it didn't come she thought it was weird but Dude she had her tubes tied...Well after she got more and more pregnancy symptoms like heartburn and urinating a lot she bought a test and it was positive. When she called her dr she just laughe ...Now she is 27 weeks and sure enough there is a baby in there. Obviously having her tubes tied didn't work.
Could you be pregnant after having your tubes tied and five pregnancy tests after your period was supposed to come all said you were not pregnant? Only if you failed to follow the instructions on the pregnancy tests. That many tests (done correctly) will not be wrong.