Can I be preganant? I hda a tubal ligation 19 years ago and my cycle is 3 weeks late, I have taken two test both results were negetive

Trust the test. Home pregnancy tests are very accurate. They are the same tests used in a doctor's office. They can detect a pregnancy 7-10 days after conception. The best time to take one is when you miss your period. If you doubt the result you can repeat it in 1-2 days. If you were pregnant the hormone level would rise enough for detection.