Pregnancy

I was on the pill for 6 months and I forgot it one day and my boyfriend came in me my periods were late but it turned out everything was fine then the pill started to mess me up and I came off it and we used condoms then one day it broke but still I never became pregnant so we started doing it without anything and I let him cum in me now (stupid I know) but I'm never pregnant my periods have been late a few times but then they come eventually ,they're late this month by 16 days (longest they've ever been late) but I've had tests done in the clinic and I'm not pregnant . Why is this ? ( sorry for the book lol)