I think I'm late?

The last day of my last period was October 8th. My cycle has always been 21 days in between. So my period would have came on the 29th 
It is normally comes right on time on the same day it's supposed to start. So it's the 1st today and 3 days late should I wait another 4 (to make the '7' day period) before testing? There Is a possibility that I could be.  I have not been stressed lately and no medications. I've been feeling like I am having Pms (emotional , easily irritated) headaches, and gastro pain every so often.