Are you late on your period???,There are 3 possible explainations here, some more likely than others,1st explaination,you got a false positive this happens somethimes so its acctually quite likely it was a faulty test,second is that you were pregnant but had a very earlly misscarriage this happens more than most people think it will probably happen to every sexually active woman at least once in her life so ive read.and third and most unlikely but still possible is that the 3 negatives are wrong,did you do the tests all at the same time,if not did you do the positve test in the morning and the negatives in the afternoon,if you did this offers another explaination in early pregnancy the hcg hormone is higher in the morning so you are more likely to get accurate results,were the tests all the same brand??? where they a pack or indivdual tests all these questions are important and will help determine what happened,If i were you i would go out buy a completely diffrent brand of test wait until the morning and test again good luck