I have also had confusing experiences with these tests. I have used the clearblue digi opk for two months. The first month I got a smiley face but then had a period a couple of weeks later.
I have used the test again this month but have tested for 7 days in a row and no smiley face at all!
I am getting so fed up with testing and sympton spotting.... someone send some babydust my way lol
xxxxx
TTC since September 2010
Chemical pregnancy in November 2010 - obviously wasn't meant to be
Keeping my fingers crossed ever since!