I started OPKs on cd 7 and am cd 9 now. I use easy@home strips from amazon and this cycle I am using a new box. I noticed these strips are showing a much lighter second line compared to my other two normal cycles at this point when I took them previously. I know all that matters is when I get positive one but can they vary in darkness until positive maybe even box to box? I am trying not to worry or stress out and enjoy TTC from now on but I was just totally curious....If it helps I have usually gotten positive OPKs at cd 14 or 15. Thank you!