Missed period

I am 13 days late on my period, but I’ve taken a pregnancy test when i was 5 days late and another when i was 9 days late, both came back negative. I have unprotected sex all the time with my long term boyfriend. I just don’t understand what’s going on though. I have all symptoms of being pregnant but maybe it’s only a mental thing... i have nausea, diarrhea, headaches, my appetite is crazy, i eat then a minute later I’m hungry again. I have backaches, matter fact, my whole body hurts a lot and almost all the time. I get dizzy so easily... i get up, then i get light headed and everything starts going black.. & i drink water all the time. My cervical mucus is either watery or an eggy white. I’m confused. Someone help😪