If you get a negative result and still have symptoms of pregnancy (missed period, nausea, breast tenderness and fatigue), wait a week and take another test or contact your doctor so you can have a blood test done.
http://americanpregnancy.org/getting-pregnant/understanding-pregnancy-tests/
Detecting Pregnancy Before You Miss a Period. Women who take pregnancy tests too early often don’t have high enough levels of hCG in their body for accurate detection. The most accurate time at which you could take a pregnancy test is if you take one around the time of your period. Negative results can sometimes occur because you aren’t actually pregnant, or because you might be ovulating later than you think.
http://www.babyhopes.com/articles/testbeforeperiod.html
A negative result can mean that you are not pregnant, you took the test too early, or you took the test wrong. Pregnancy tests vary in their sensitivity (how soon they can detect the hormone hCG), and you may not have given your body enough time to produce enough hCG hormones that will show up on the test.
http://americanpregnancy.org/getting-pregnant/understanding-pregnancy-tests/
Blood pregnancy tests are always the most accurate way to determine whether or not you’re pregnant. Results from these tests are available after 24 hours and can be taken as early as eight days after fertilization occurs and hCG is present in your body.
http://www.babyhopes.com/articles/testbeforeperiod.html
After giving birth, hCG may take up to 3 weeks to return to normal levels. If you test during this time, it’s impossible to know if a “Pregnant” result is caused by a new pregnancy or by hCG from your previous pregnancy. In this case, we would recommend that you contact your doctor.
http://www.clearblueeasy.com/general-questions-about-pregnancy-testing.php
All Clearblue® Pregnancy Tests are sensitive enough to detect hCG in your urine from the day of your expected period1. Additionally, you can use Clearblue® Pregnancy Tests up to 5 days before your missed period2, although the pregnancy hormone levels in your urine may not be high enough to be detected. If you test early and you get a “Not Pregnant” test result, we recommend you test again when your period is due. Tests that allow women to test earlier than 5 days sooner than the missed period can be prone to produce false “Pregnant” results in non–pregnant women. Clearblue does not compromise on accuracy.
http://www.clearblueeasy.com/general-questions-about-pregnancy-testing.php
Urine tests or home pregnancy tests are around 97% accurate when done correctly. Home pregnancy tests are great to use because they can be done at home, they are usually low in cost (anywhere from $7.99 to $19.99), private, they give a fast result, and are easy to use.
http://americanpregnancy.org/getting-pregnant/understanding-pregnancy-tests/
There are highly sensitive pregnancy tests that can detect pregnancy up to six days before ovulation, which is around eight days before your cycle begins. However, this increases the potential for false negatives.
http://www.babyhopes.com/articles/testbeforeperiod.html
Most doctors recommend that you wait until the first day of your missed period before taking a urine pregnancy test. This is usually about two weeks after conception. However, some tests are more sensitive than others and can be taken earlier.
http://americanpregnancy.org/getting-pregnant/understanding-pregnancy-tests/
It is recommended that you wait until you have missed a period to take a home test. A missed period is often one of the first signs of pregnancy. If you cannot wait that long to find out and you know the day you may have conceived, then the earliest you can take a test would be 14 days from possible conception.
http://americanpregnancy.org/getting-pregnant/understanding-pregnancy-tests/
when can i start taking pregnancy tests
You can start taking pregnancy tests would be 14 days from possible conception. You can start taking pregnancy tests 14 days from possible conception. The earliest you can take a pregnancy test would be 14 days from possible conception.