period is 11 days late

I am only 17 very regular periods I have been since I was 13 I had unprotected sex twice with my boyfriend and now I missed my period I am 11 days late I took a hot and it was negative I spotted for a day I thought it was AF but nobody brown color blood like it's old I also had unprotected sex the day it was due but I had nothing I finally got a blood test and the doctor said it was negative any clue what's going on