You may not be able to have children. Try having sex a few more times and if that doesn't work, see a doctor and ask about why you can not have a child. If you can't have a child but still really want one, consider adoption. It is always an option. Best of luck and don't forget to follow me. (:
Read the book "Take(ing) Charge of Your Fertility". It is an awesome boom that explains everything you need to know to get pregnant, or to avoid it. It's a very fast read. It worked for me and several I have recommended it to!