i was suppose to start my period on the 10th or 11th i had sex on the 8th & 15th. On the 8th he didnt put a condom on til the middle of sex but he ejaculated in the condom not in me. the 15th i didnt use one at all, im on birth control and i always start my period AFTER the white pills. and im having lower right back and right pelvic pain, we've havent used condom's lots of times and never came up pregnant but it is now the 20th and i still havent had my period, is this common? is there something else wrong because of the pain? HELP!!