I'm so confused with my opk's this month. Help?!?

This is my 4th round of Clomid, 150mg. I had what looked like a positive ovulation test yesterday (with First Response-non digital), but when I tested with CB Easy digital in the afternoon, it was negative. Same thing this morning (tested at 6:30am), line was even darker on First Response this morning, but CB Easy digital still says negative (tested again at 11am). Anyone experience this or have advice? Thank you!