Probably that you are pregnant, and your urine just didn't have enough hcg today to show positive, or the test strip was defective today, or that it just wasn't as sensitive as yesterdays. Do some research on these test...you will find that even though they say 25 mlU/mg......that is the least sensitive they will be. You can buy one of those 5packs, where there is 5 in a pack, and 3 might turn up pos and 2 neg, or 1 pos and 4 neg.....indicating that even though they are all "the same", some are more sensitive then others. It's accidental in nature, but it happens. ALOT! I would bet if you test again a couple more times, you will get more positives. And it's much harder to get a false positive then it is a false negetive. Also, make sure your pos wasn't an evaporation line. This is when a test was neg, but after it sits a while, a light line appears......after the 10 minute testing window. Good luck to you.