Ruby-Not to make you worry or cause you anxiety, but actually, if the OPK was a true positive on day 13, I would almost be concerned that you inseminated too late, not too early. Once you get a positive OPK, stop checking. It is only the first positive that means anything. OPKs will generally stay positive for a day or two, but that doesn't mean anything. Once you get a positive you should ovulate 12-36 hours from the first positive. If the OPK was just starting to get positive on CD 13 and 14 and wasn't truly positive until CD 15 that's a different story! Here's to hoping that was the case!