Late w symptoms but negative test?

Okay. So my period is officially a full week late, & period is usually off just a day early or late. Never a full week. I do have unprotected sex, and there was a time a week or two after my last period that my boyfriend had cam inside me twice, and somehow had forgotten to get a Plan B.

I have been feeling nauseated here and there, fatigue, (& sorry for the tmi) diarrhea, had cramping right before my period was suppose to come (which I always have before it), minor headaches, & also feeling dizzy every once in awhile throughout the day.

So this led me to take a test at 3 days late, got a negative. Waited around 72 hours to take another, still negative. Is there any other reasons why my period could be late? Any possibility that it was a false negative? I thought maybe I’m just sick, but I feel fine for the most part when I’m not having any symptoms.