So I know that after you have sex for the first time, that it may cause your periods to go crazy and be late by a few days, I'm only 2 days late, but I was with my bf, and his little sister who is like 5, kept calling me mommy, and I broke down crying. We thought something was seriously wrong. So we took a test and it was negative. I do not want any children right now, so is a false negative possible?