Confused...OPK tests

Ashlie
Hi ladies - does anyone have any idea how opk clear blue advanced digital kits work? My cycles are regular and I usually get blinking smiley on CD14 followed by steady smiley on CD15 while monitoring my bbt to Make sure I ovulated. 
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​My period is due tomorrow and for past 3 days I m getting blinking smiley which means elevated estrogen levels. But as far as I know estrogen levels drop before period. Any idea what's going on?