8 day late period..

So my last period ended June 28th and my new one was supposed to start July 23rd. I Began spotting two weeks before my next period and it went on for a couple of days. It was brown and some light pink. My boobs usually get sore before and during my period but this time I’ve had no soreness until now and I am very late. My bf and I are sexually active and had sex a week or less prior to the spotting, we checked the condom but it didn’t break and I took a test 4 days after my missed period and it was negative. I am now 8 days late and have never been more than a day late. What could it be?