I have had to use the morning after pill (emergency contraception) twice in 2 weeks. is it as effective the second time?

Yes, but a better : Plan is regular contraception. The "ohmygosh" we need Plan B is a terrible plan. Be good to yourself.

Yes: It is equally effective but you can imagine a doctor's question.... Why not find a more reliable form of birth control? If you are okay taking pills, consider the birth control pill. Taken each day it will prevent 96% of pregnancies in a woman sexually active over course of a year. Good luck!