A small amount of bleeding after 3 days of intercourse is not certain to be pregnancy. There are many reasons why a small amount of bleeding occurs 3 days after intercourse, the most common reasons may be the following: 1. It may be the arrival of the menstrual period or ovulation bleeding, these are physiological phenomena. The bleeding is relatively small at the beginning of the menstrual period, and if it is the arrival of the menstrual period, you will not get pregnant. But if it is ovulatory bleeding, there is also the possibility of pregnancy. Ovulatory bleeding is caused by the decrease of estrogen level in the body after ovulation, which causes the endometrium to shed and bleed. The bleeding during ovulation is relatively small and has little effect on pregnancy.2. It may be caused by organic gynecological diseases, such as cervical or vaginal mucosal lesions, uterine fibroids or adenomyosis, which may cause a small amount of non-menstrual bleeding.3. Endocrine disorders may also cause a small amount of bleeding, resulting in non-menstrual bleeding or irregular menstruation, very little menstruation, etc. It is suggested that gynecology combined with vaginal examination, pelvic ultrasound examination, etc. to further determine whether there are gynecological organic lesions.