OPK back & forth

I have only recently started tracking my ovulation with tests, I ordered the MomMed test strips. I have been testing since the 23rd, this is our first time TTC. My first test I took in the evening about 6pm, it was a darker color but not as dark as the control line, I have read that it's better to take the test in the after but didn't want to really take them that late. So I've been testing when I come home for lunch & they are very faint lines which I know are negative but the last couple days I decided to test again in the evening after I get home. My evening tests are way darker then my afternoon tests. Can anyone help my understand why that is? I'm so confused on this stuff which is making TTC more stressful then it should be.