Another opk question...help??

Soo saturday afternoom I took an opk and it was fairly dark so I figured I would get my pos on Sunday, but instead it was ligther and negative. I was crampy sunday morning and had a slight temp increase(from my usual 97.8 to 98.3) so I'm thinking I may have ovulated in the night? It was at least 24 hours in between sat and sun tests. I've also continued to test and have gotten negatives. I'm new to this so I'm just asking for advice so I can pinpoint my ovulation. Also confused becausr glow and ovia have my fertile week being the 3-9. Thanks for any advice!!