I have been taking OPK's (ovulation predictor kits) since CD 10. I am now on the eve of CD 16. All have had varying degrees of faint lines until this morning at 9am, when the line was almost as dark as the test line. I took this as an 'almost-positive', thinking that if I tested again tonight/tomorrow morning it would be definitely positive.
Just tested again, 7 hours after the above test, and it was back to being super-faint 
. What's up?! I thought the LH hormone was supposed to strengthen over the course of the day, so I was expecting a nice thick dark line this evening 