clear blue question

Ashleiy
I use the digital clear blue. I am on CD 15 and yesterday around 11 am I got a solid smiley. Peak fertility. I usually ovulate around day 16 or 17 so on track BUT as many of you know after you get the peak the test is useless for 48 hours. Well this morning I was just curious and took a regular cheap opk and it was negative. Could my surge be over ? I usually ovulate 48 hours after positive opk. So I'm just confused on why the one this morning was negative. We BD twice yesterday and will tonight. Any advice ?