No, it is not possible to get pregnant if you are already 13 weeks and 4 days pregnant. Once fertilization occurs, the egg implants in the uterus and pregnancy begins. Therefore, any sexual activity after that point will not result in another pregnancy. It's important to note that contraception should still be used even during pregnancy to prevent sexually transmitted infections (STIs). If you have any concerns or questions about your pregnancy or contraception options, it's best to consult with a healthcare professional for personalized advice.