I had intercourse on the first day of menstruation, can I get pregnant?

Socorro Doctor !!! I have a very big question. I had sex on the first day of menstruation. Menstruation for 4 days. I'm not sure the condom did not burst. Today, 07/09/11 at 9:00 p.m., it will take 72 hours for the act to take place. So until tonight I still have how to take the morning-after pill. Only I have an active sex life and I'm afraid that I need to take the morning-after pill on another occasion. I already took the morning after pill, 5 months ago, I did not want to take it again because I read that it is losing effectiveness every time I take it. But if I have to, I'll take it. I do not take anti-conception. I would like you to help me, because I do not want to get pregnant. In August I menstruated on 8 and on September 4. Is there any possibility of getting pregnant? Should I take the morning-after pill? (remembering that I'm still menstruating) Please, Doctor, help me !!! Answer me as soon as possible !!! Thank you God bless you !!!