I had my tubes tied 13 yrs. Ago along w a partial tubal 15 yrs. Ago. I have a normal period on the 16th of every mo th which lasts 5 to 8 days. My last period this month sept. 16th only was heavy for 2days and spotted for 1 then I was done. Pregnancy test said negative could this be a false negative? Could I be pregnant?