OPK help

Monica • I`m a 30 year old military wife and mother to our 9 year old son, Rylan and daughter, Maci who is 4.
Okay so usually each moth I have no problem telling when I get a +OPK because the line is always as dark as, darker than the control line, or lighter significantly. This moth (3rd month tracking) I am having trouble telling from yesterday morning. I'm putting my first twos this of positive's pictures so you can see how they usually are (highlighted in yellow) and then the last picture will be what I have so far for this month. I'm on CD 17, I usually get a pos OPK on cd 20-24. But yesterday morning on cd 16 (am) 1-28 it looks really close to positive. I know that morning in the 5 minute frame that it was slightly lighter than the control line but now I'm wondering if it wasn't? I'm so confused. I was wanting to try BD every other day until I got a pos OPK but now I'm wondering of I Should start doing it every day like usual? Also, I usually get at least two +OPK's and they have all been light again since yesterday morning. Sorry this is so long...hope someone can help.​month 1 ^
​month 2 ^
​month 3 ^ this month. 
​a closer pic ^