Did I miss my ovulation?

This is only my 2nd month using opk’s. Last month I found it very simple as I got a very clear positive (the test line was darker than the control line). This month however I’m not so sure, the kits were gradually getting gradually darker just like they did last month, but then the day after I got a very close to positive test (which was Thursday), they started getting lighter again and by Monday the test line has completely disappeared. Is it likely that I missed my peak? My periods are irregular but I was roughly expecting a positive result end of last week/beginning of this week. Any help would be lovely xx