No signs of period

Laura

I was originally due on my period on Monday 28th, but as yet no sign. I keep putting on glow that my period is late and it just moves on the expected date by a few days each time. I have done a few tests and they are showing up as negative but not sure on when to test or when to expect my period as never sure long my cycle is as it alters each month (never been this long though) any help advice would be appreciated. Thank you.