I need OPK specialist!!

Jenny • New Mommy to Jolie, Veterinarian and Husker Football Fanatic❤️
Ok so weird question ladies.  Tested last night with digital CBE ovulation kit at 8 pm and it was neg.  BD anyway last night.  
Tested at 7 am this morning and  it was a positive + smiley face.  
Got home from work at 1pm this afternoon and tested neg?  How is this possible?