18 days late unclear results!

I'm 27 and trying to get pregnant with our first child. My period is 18 days late, I'm quickly irritated, boobs swollen, nausea from time to time and very frequent headaches. I got off birth control 6 months ago and was regular up to this point. I took this pregnancy test the week of my expected period but I have taken many tests since including today that's shows negative. The following is very faint. Any help or advise would be appreciated!