I've took a pregnany test wednesday morning and it was a positive and then took another one later in the day and it said negative what is that mean ?

Positive: Usually a positive is positive. False negatives are more likely than false positives. Having said that, however, i would take another test or see a doctor for blood test. It is possible that you were pregnant, your blood levels or hormone of pregnancy were dropping and the negative was truly negative. Take another test, though, to ease your mind.