Help, when did I ovulate?

So this is the first month this had happened. Usually I ovulate around day 13-15. I will usually test positive opk before I ovulate. This month it's completely different. I am on day four of positive opk tests. I put a picture up for it, top test as day 13 and it goes down from there. I know today is lighter but I think still positive. Fertility friend/basal temp is telling me that I ovulate before positive opk test. How did I ovulate before a positive opk test? Or have I still not ovulated? Any comments are appreciated! Thanks!