Late period but BFN

I am currently 4 days late on my period, we have started tracking my ovulation using clear blue OPK. I took a pregnancy test (clearblue) first thing this morning and it is negative.....still no sign of AF. I have the flu also and have been feeling very emotional. I am experiencing no premenstral cramps either. Just wondering if anyone else has experienced this. Any stories shared would be greatly appreciated. We lost our first baby last year due to an ectopic pregnancy and so desperately want another. But nature just doesn't seem to be on our side :(