OPK Help?

Is it normal for your opk to get darker but then getting lighter again with no peak/positive inbetween? I got a darker test the other day, which I thought meant I would start getting closer to my peak, but then by the next test that was 11hrs later, it was lighter again with no peak/positive yet. Is that normal? I thought it was supposed to keep getting darker until I got a positive? I got my IUD out on the 6th and had a period from like the 7th-13th. Or does that not even count as a period since it was right after IUD removal (but it was heavier than just spotting, it was a mediumish flow)? Sorry for all the questions, new to all of this! Thanks for any help!