It is absolutely normal for semen to leak out of the vagina after a vaginal intercourse. On an average, the semen contains more than 20 million sperms per ml. Given the fact that only one sperm is needed to fertilize the woman's egg, I guess you should not worry about some semen leaking out. You need not lie still after the intercourse for any period of time. The sperm deposited in the vagina swims up through the women's mucus and reaches the uterus within minutes of the ejaculation and the rest of the semen leaking out does not matter as much.
Having said that, since you are trying to conceive, I must also mention that with regular unprotected intercourse only about 25% of couples conceive spontaneously at the end of 1 year of trying to conceive. Hence, if your wife does not get pregnant immediately do not get very disheartened by the same. All the best to you. Hope you embark on the journey of parenthood soon.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.