why does almost positive opk get lighter?

[iheartmyfamily]

Ok, so this is the 2nd month this happened. it happened on my january cycle too. i got an early high on cbfm. i chalked it up to these herbs i'm taking bc last month my o date was earlier too and cbfm only gave me 3 highs before my two peaks. so yesterday and the day before i had highs on my monitor at cd 11 and cd12. woohoo! my opks were nice and visible but not as dark or darker than the control line. today i've taken two opks and the line is barely visible. was my body gearing up to o and then changed its mind? does this happen often to u ladies?

[karmab]

it happens all the time, or else we have lh levels that are high enough to almost register as a pos opk, but not the surge that puts it over the edge. either that, or you just missed it- that can happen too, especially if you only test once a day, cuz it can come and go within 24 hrs. whenever i get a close to pos, i will test every 6 hrs, but sometimes it goes from nothing to blaring in less than a day.