positive than three days later a negative???

Has anyone ever had a positive test than took another one and it turned out negative? I took a second one because I was either spotting from implantation or getting my period. I have been monitoring my spotting since 5:00am this morning and it was extremely light, then it turned red and got a little heavier so I took the test and it came back negative... HAS THIS EVER HAPPENED TO ANYONE ELSE?