OPK help!

Ladies I am so confused, has this ever happened to anyone before? And what could it mean? Okay, so I got my first pos opk on CD 14 I tested positive until late in the after noon on CD 16 then it was negative. I did not test on CD 17 because it already had turned negative. But then tonight on CD 18 I took a test (like many I am addicted to poas) and it looks positive to me! What do you think, and what would that mean?