Welcome to HCM,
There is no possibility of getting pregnant through intercourse on last day of menstrual period. Menstrual cycle includes menstrual period also, while gap denotes period between two menstrual periods. In your case if menstrual period lasts for 3 days & we add it to gap of 18-20 days, we get your menstrual cycle of 21 to 24 days. Ovulation generally takes place 14 days prior to next menstrual period. Thus in your case ovulation is expected between 7th & 10th day of menstrual period, which can be further confirmed by use of Ovulation Prediction
Kit. To increase chances of pregnancy
, you should prefer sex on & for a few days after ovulation. T. Neomercazole is not expected to exert any effect on sperm production. But you should get semen of your husband tested.
Wish you good health & early conception,