Since there is no such thing as a "false positive" result... you're pregnant. If a test comes back later with a negative result (false negatives are possible)... then its just a bad test (something must have gone wrong, or the test is defective).

If you had two positives and then a few days later you have a negative, it is likely a chemical pregnancy. ------------- Understanding Chemical Pregnancy Many women have never heard the term chemical pregnancy until a doctor uses the term with them. Chemical pregnancy is a technical way of referring to a very early miscarriage. With the more sensitive pregnancy tests now on the market, a woman can get a positive test result before her period is due, but a miscarriage occurs before a doctor is ever able to detect a heartbeat or see the baby on an ultrasound. While the early test results are great for some, they mean that many women are feeling the loss of a baby that they might not have ever known about had it not been for the early pregnancy test. Luckily, most chemical pregnancies occur without the mother knowing that she was ever pregnant. Despite the term not being well known, chemical pregnancies are very common, as some experts believe that up to 60% of first pregnancies end in a chemical pregnancy without the mother ever knowing that she would have tested positive for pregnancy! This is sort of disturbing on one hand, that so many women have been pregnant without ever knowing it, but at least most of those women do not have to go through life wondering what went wrong, and feeling the loss for what would have been their child if it had continued to develop. http://www.thelaboroflove.com/articles/are-pregnancy-blood-tests-ever-wrong/