Pos OPK then NEG on the same day.

I took a clear blue opk this morning at 10am and it was a smiley then I took another at 7pm and it was negative. I’m so confused.

I took the opk two days before and each day they were just circles although yesterday I took one first thing in the morning. I didn’t take one last night. So maybe I missed the surge yesterday?? Did I have a quick surge or it ended today? Should I BD tonight and the next few days?? This is my first time keeping track!

Also: my period started on July 9 so this is technically day 11. I am feeling slightly crampy and nauseas today. But CM is dry/clear.