What Causes Missing Periods?

Hello, I am late just one day on my period, took a pregnancy test came back negative(I imagined I saw a faint second line) but says dont read after 10 minutes. Well, I have been so tired last 3 days did not even change my clothes or go outside. My cervix (sometimes seems high and soft) sometimes seems in the middle and soft/hard?? urinate slightly more, sometimes eggwhite discharge,sometimes cramy yellowish, sometimes white with streak of red? I only had sex the second day after my last period(once) can I be pregnant or is this something else?