S.,
You have received wonderful, encouraging responses: evidently it is not uncommon to obtain a false negative response. My only additional thought is that, in your enthusiasm, perhaps you are a bit over-eager (you might read over-anxious) in testing when you are one day late. If anything, I think that the self-imposed "stress" of knowing instantly might might work against conception. If you are pregnant, you are; if not, you and your husband will still enjoy the process of your becoming pregnant. So just RELAX, forget about testing "immediately" and let nature take its' course. In the Bible, patience* is not only a gift of the Spirit, but is cited as a factor in God fulfilling His promise to bless Abraham and Sarah with a much-desired child:
Hebrews 6:13-15 - "For when God made the promise to Abraham, since He could swear by no one greater, He swore by Himself, saying, "I WILL SURELY BLESS YOU AND I WILL SURELY MULTIPLY YOU." And so, having patiently waited, he obtained the promise."
S., be encouraged. You'll know VERY early on when you become pregnant, because you are trying, have (apparently) successfully given birth to 3 girls and are eagerly anticipating another desired pregnancy. So what if it is 10 days, or even 20... before you "confirm" the realization of your desires?
Wishing you success in your aim and joy in the process,
K.
* Scriptures on patience - 2 Corinthians 6:6; Galatians 5:22; Ephesians 4:2; Colossians 1:11, 3:12 and 2 Timothy 3:10