My period is late, multiple tests are telling me Negative..

Jessi
I am 24 days late. But for the last three days, after me and my fiancé have sex, I notice that whenever I use the bathroom, I have a slightly pink discharge and it goes away within an hour or so. I have taken 4 tests since the day AF was due and I have received nothing but negatives... help.. I have no symptoms of pms and a slight case of nausea in the morning whenever I wake up.