I'm 21 days late on my period, but negative pregnancy test. but i'm nauseous, have headaches, bloated stomach, and several other pregnancy symptoms.

Look 4 other cause : Home pregnancy tests are very accurate. They are the same tests used in a doctors 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.