No period, negative test, what could it be?

Hi all, I was due for my period 11th this month & didn’t get them, then I had unprotected sex the 13th - he finished off in me & there was a lot of it..I’ve done a clearblue pregnancy test on Wednesday, but it came up negative, I’m booked in for a doctors appointment next Tuesday to do a urine/blood tests, I was put on the pill last year to re-trigger my periods & I had been getting them every month since New Years, apart from June as it was a very stressful month for me, I can’t tell whether it’s PCOS as to why my period hasn’t come this month (which I don’t know how if it is as my periods have been pretty regular since coming off the pill) or if I’m in the early stages of pregnancy. Someone help 🤷🏻‍♀️