pls help. 12 days delayed yet negative result

my bf and i had unprotected sex during my period, sept 25. my last period was sept21. we had sex again on oct 14th but he didnt ejaculate on me. yet until now, im not having my period. i was expecting it since oct 18. i had preg urine tests last oct 25, 26, 27,28 and this morning(im too anxious!) and it was all negative... am i preg? how would i know? whats my chance of being preg? ty