If you had sex again within 2 hours of taking the Plan B, then you should be covered for that sex. It is recommended that another dose of Plan B be taken if you have unprotected sex again. Plan B is not 100 % effective at preventing pregnancy and so it not considered effective to be used as contraception such as condoms or taking the birthcontrol pills. Plan B works by delaying the ovulation so that the sperm in the body die before meeting the egg and Plan B also temporarily alters the lining of the uterus so it is less likely for a fertilized egg to implant. Plan b does not cause an abortion so if you are already pregnant it will not end a pregnancy. Within 3 weeks or 21 days of taking Plan B, you should have a bleed like a period. If there has been no bleeding in that time, please take a pregnancy test at a clinic near you. Let us know if this does not answer your question or if you have any more questions or concerns.