My period is now a few days late, pregnant?

my last period was the 16t november , my period is now a few days late , i had sex wit my boyfriend and we use the withdrawel method , im not using any birthcontrol and he did not come inside of me , i have been having lower back pain now and again , i had a thick white discharge that i have never goten before and feel mild cramps on the side ofmy lower part of my stomach and my nipples just started to be sore yesterday when i touch it , i tok a pregnancy test its negative , what is happening to me ? am i pregnant or what ? please help me