Late or Missed?

My period is now 6 days late and it's been 23 days since the last time of intimacy before i ovulated (or so according to my calendar. We had sex 1 day before the start of my ovulation). Ten days after intimacy I tool an hpt and it was negative (then my SO and I did the horizontal tango again) I'm kind of anxious and I have been testing since the first day of my "missed period". Yesterday I took another hpt and it was still negative. I have been experiencing "pregnant" symptoms but then it suddenly stopped when I passed a blood clot 3 days before the start of my supposed period.

My SO told me I may have been testing too early or I'm stressed out leading to me getting negative on the hpt.

Has anyone experienced this before? Were you pregnant?