What can cause a false positive on a store bought pregnancy test?

There are few things that can cause a false positive. those include: Gross amounts of protein in the urine, fertility drugs,use of cocaine, certain types of cervical cancer, exposure to mouse feces (though this usually this kind has to be picked up on a blood test because amounts are so low), and contrary to what many belive, if you read the pack your pills come with it does say that on VERY RARE occasions pregnancy tests can give false positives if taking birth control (but only with certain kinds). But these are all extremely rare and 995 of the time the positive is real. So most likely you are pregnant. Sometimes if you are even off by an hour taking your pill, it can leave a window open to get preggers. This is most likely what happened.  more