Cd 17 and still no pos Opk!!

don't know what is going on...usually I'm like a clock with ovulation Cd 14 of a 28 day cycle but this month iv been testing an the lines are still not as dark as the control line. I tested Wednesday evening and the test looked like it was getting darker but then when I tested Thursday evening the line was hardly there...just took one now 00:24am Friday morning and it's slightly lighter than the control line...why is this month being so weird! hope it's just a one off. We have been bding every other day so hopefully we have done everything we can