"i am on the pill trinessa but took an antibiotic, cyprofloxacin, for a urinary tract infection a week before having sex with my boyfriend. he didn&#039;t use a condom and i heard that antibiotics can make the pill less effective so i was super paranoid and scared that i would get pregnant. so about 16 hours after sex i took next choice one dose. right after i took it i had a headache but that&#039;s it. didn&#039;t have any other symptoms for several days after. since i am on the pill i know exactly when i am supposed to get my period. i felt menstrual cramps and fatigue for a couple of days before the day my period was supposed to start. i had light bleeding and cramps on the day it was due. relax &amp; good luck"