SUPER LATE

So the first day of my last period was December 6th. I haven't had my period yet and I am a little more than 3 weeks late now. I am normally irregular and my period will sometimes come 1 week early or up to a week and a half late. I took a pregnancy test almost a week ago it was negative. I have noticed more sensitivity to smell, today had cramping and some nausea and still no sign of period. I plan on testing again tomorrow or Friday. If it's negative again, is it possible for me to be pregnant and it not being showing up???