if you do it in the morning first morning urine is accurate however water dillutes hormone if you drink alot of water it will dillute the hormone also it could be a chemical pregnancy
I have actually had a false positive before, freaked out thinking i was pregnant, went to the gyno and foung out i wasnt preggers. take a few tests before you decide to go to the doctor. there still is a chance that you could be pregnant though.
take a few tests, maybe three. that one in the morning, one at lunch, then anoth the next morning. are you late or having symtoms of pregnancy? untill you know for sure, just treat your body like you are pregnant, like dont drink alcohol or anything.
What kind of test was it (blue or pink dye) and how long did it take to show up. Also, when did you take the tests (morning, noon or evening). Did the test line have any colour to it as well, or was it a shadow/grayish looking. It could have been a true positive and you just didn't have enough hCG in your urine the next day to make the test show positive, or it was an evap line. Repeat the test in a day or so with first morning urine. It would also be advisable to use first morning urine, as it has the highest concentration of hCG in it.