period late, negative test

My period is currently 4 days late. Took two tests, both came back negative. I've been experiencing tender breasts which is unusual for me and none of my usual pre-period symptoms. My period is very regular 
I had my first round of The HPV vaccine (gardisl) a week ago. Is there any chance this is what's causing my late period? Has anyone experienced this after recieving the vaccine? Or could I well and truly be pregnant?