What Causes Missed Period After Intercourse?

Hi Doc i'm 27yrs old. My issue is missed period. My last period was on May 17-24. I had sex with my boyfriend on May 29. For about 2 mins he penetrated me without the condom then he put it on. On June 7 I had sex with my ex (mistake) and then took postenor 2 on June 8. My period is late, it should have came by June 17. I have been having fluctuating pre-menstrual cramps but no blood since then. I have taken 2 pregnancy test which says negative. Questions: Could i be pregnant? Could my period be late because of the pill? Could my cycle have changed bcuz both penis sizes are far different ay my ex is 9.5 long when erect.