Thank you for your question. Even one drop of semen contains millions of sperm so you need not be concerned if some of it leaks out of the vagina. You only need one sperm to get pregnant. You also do not need to put a pillow underneath you or lie upside down for any length of time. By the time your husband withdraws his penis the fastest healthiest sperm are already inside the uterus making their way to the egg if you have ovulated. You can see videos about conception on you tube that explain this process beautifully and it will put your mind at rest. You need not stop intercourse any time just as you need not time it. The main factor is being relaxed and being in a state of positive expectation. Your body follows your mind's instructions very closely so it will help to always expect the very best for yourself. With best wishes for your pregnancy