Are my chances high of being pregnant ?

Hello everyone, so my period has come every month like clockwork but this month in late by 8 days now. I don't know what's happening, I have a lot of lower back pains, a small bit of tenderness in my breast, a little more tired,and instead of my period, for the past few days I've been getting white discharge instead of blood. But I've taken three at home pregnancy tests and they've all come out negative. How likely do you think it is that the tests are coming out as false negatives or something ?