There are some positions your wife can adopt after sex that supposedly improve the chances of conception. I have no idea if they really make that much difference.
It can just take time for this to happen, but if you are worried I would suggest both of you see a doctor to have your fertility tested.
Finally (and please don't take this the wrong way, I know absolutely nothing about you, your wife or your circumstances), it is possible your wife does not want a baby quite yet, but can't bring herself to tell you, and has been taking The Pill without you knowing. It wouldn't be the first time in history.
The Content on this Site is presented in a summary fashion, and is intended to be used for educational and entertainment purposes only. It is not intended to be and should not be interpreted as medical advice or a diagnosis of any health or fitness problem, condition or disease; or a recommendation for a specific test, doctor, care provider, procedure, treatment plan, product, or course of action. MedHelp is not a medical or healthcare provider and your use of this Site does not create a doctor / patient relationship. We disclaim all responsibility for the professional qualifications and licensing of, and services provided by, any physician or other health providers posting on or otherwise referred to on this Site and/or any Third Party Site. Never disregard the medical advice of your physician or health professional, or delay in seeking such advice, because of something you read on this Site. We offer this Site AS IS and without any warranties. By using this Site you agree to the following Terms and Conditions. If you think you may have a medical emergency, call your physician or 911 immediately.