Positive test no pregnancy ?

So back story, i had the paragard iud for about a year it was expelled in June, wasn’t sure we wanted to try right away.. took plan b June 10th got my period 3 days earlier than expected and it lasted 7 days which is unusual for me. It went away after those 7 days then i got it again 2 weeks later and it lasted 9 days. (I know that’s a side effect) i got a blazing positive OPK on the 25th of July we had sex with no protection the day before and almost every day after including the day of the positive OPK . I could’ve sworn i would get pregnant but i got AF just as glow predicted. I’m confused as to why 😔 im pretty regular and get my period every 28 days