Ok so I started using opk this month for the first time well I got what looked like was a positive ( the brightest one I got of all of them) on the 13th and 14th well I got a different brand on the 14th that night and it was just showing a control line so it made me think the 13th or 14th (morning) was actually my O day well I took a few more leading up to today which was also just a control line. I took one today and got this. Why would it change from no test line to a faint test line. The other pic is from the days before.