Is it at all possible?

I have taken 3 pregnancy tests... One 5 days before my period was due, negative. One the day my period was due, negative. and then one 3 days after my period was due, negative. I decided I wasn't pregnant and that I was probably just coming down with a flu and my period will show up. I have now completely missed my period and am 7 days late. No spotting. no nothing. I was checked for pcos not that long ago and it came up completely fine. no pcos. I'm not particularly stressed out and nothing in my life has changed. I have a doctor's appointment for Thursday to get it checked out... but has anyone experienced a negative test after their period was due and turned out to be pregnant? I can't figure out why my period would be this late when it comes every month like clockwork.