Pleeaseee help. Opks don't telling lies?

[Clairerob]

I went to the loo about 45 mins before I went again and on my 2nd visit my opk was deffo positive as the line was a little stronger than the test line. We dtd then just to double check I did a digital opk after holding my wee for 2-3 hours and it gave no smiley face. What on earth is going on? Has anybody else experienced this? How can it be sooooo positive 2-3 hours beforehand and nothing strIght after? xxx ps I'm 8 days after my period ended