I would say that you probably are pregnant (and I am very sorry for giving you hope if you are not). Test again in the morning with your first morning urine and see what happens. Meanwhile, read the instructions on the test very thoroughly to see when the read is accurate. Results read after the 10 or 15 minute window are generally regarded as inaccurate.
For knowledge and entertainment, go to www.peeonastick.com
Edit: I just went to peeonastick and they have two brands of tests that say if they have 'disappearing positives' it is the same as a negative result. There is tons of information on this website.
Edit again: OK, I found this on the POAS website:
"13. The line disappeared after the time limit! Is it still positive? Please see Current Issues & Alerts for information on this ongoing problem with Answer Early and First Response Early Result tests.
A positive result will generally stay positive for 48 hours. Some very faint lines may fade and become difficult to see, however. Note: sometimes a line will appear briefly as the dye in the test passes over the area where a positive result would show. This is not a positive result.
My suggestion: as soon as urine is applied to your test, set a stopwatch for 9 minutes, 45 seconds. Place the test on a flat, dry surface and walk away. When the alarm goes off, read the test from the same distance you would read a book-- allow 15 seconds to examine the test. If there is a pink line (or blue, obviously, if your test uses blue dye), you are pregnant. If there is no line at the 10-minute mark, you are not pregnant or you are testing too early and there is not enough hCG to be detected in your pee. Note: women who have experienced the current "disappearing positive" phenomenon often had a positive result at the 10-minute mark, only to have the line disappear minutes or hours after that. The vast majority of these women have not been pregnant.
If you really get what looks like a true positive, and it disappears, I suggest calling the manufacturer and asking for their input. They may compensate you for the test as well."
Baby dust!