Girls, explain?

Girls, explain? Cycle is 30 or 29. Just judging by ovulation tests, it was on Day 14, but the calendar shows my type should be on Day 17. But I have this feeling that even the tests are misleading on Day 15. I take a test and the second strip is already very pale, today I did another one too, also pale... Although today it's really pulling down low... Nothing makes sense, can't it just show up like that first day, then a new test and almost invisible?)