Postinor 2 is a post-coital contraception pill which is to be taken ideally within 24 hours but not later than 72 hours of the unprotected sexual intercourse to prevent pregnancy.
In fact, woman releases her egg only once during a menstrual cycle and that day is 14 days prior to next period. An egg has a life of 24 hours while the sperms are active for 72 hours. Hence a period of about one week around the day of egg release is a fertile window. Unprotected intercourse during this period is more likely to result in pregnancy.
Intercourse during menstruation: During this phase of the menstrual cycle, there is no egg present for fertilization. So there is no possibility of any pregnancy by the intercourse during bleeding phase of the menstruation. Hence, there was no necessity of taking Postinor 2 after this intercourse.
Postinor is a hormonal medicine containing 1.5 mg of Levonorgestrel, which is a Progestational medicine. Progestational medicines do minimise or stop the bleeding from the uterus. Hence, your menstruation will cease. Now after 4-7 days later, you will have withdrawal bleeding which would be just like your normal menses.
So you need not be worried about the possibility of pregnancy. However, to have sexual intercourse during menstrual bleeding is not safe for the health of the woman. Blood is a very good medium for the bacteria to grow. Hence intercourse during menstrual bleeding does carry a risk of infection. Moreover, the tissues in the reproductory tract of the woman are in the tender stage of growth during this phase of menstrual cycle and may carry the risk of getting converted into cancer cells due to the intercourse done at this stage. Hence, please do not perform sexual intercourse during the bleeding phase of menstrual cycle.
As far as this intercourse is concerned, you cannot be pregnant due to such intercourse.