am i pregnant ?? .. what's going on

nikole
okay so i was supposed to start my period on february 18th, but i didn't and i wasn't suppressed cause i've been having unprotected sex, so on the 2nd day febuary 20th i took a pregnancy test and it came out negative. so i though what's going on my period is never late so now it's february 22nd and i'm bleeding only a little? does anyone know what's can be happening ??? please help