I had sex on the day I was supposed to start my usual period. The condom broke and I had bought a plan b pill. I took the pill 18 hours after having sex. Is the plan b still highly effective? It was 3 days ago when I took it & I still haven't got my period. Does the plan b cause late periods? And if so how long should it be till I start my period? Thank you for whatever answers you may have!