It is estimated that one in seven couples will have difficulty conceiving at some stage in their reproductive years. I would recommend you begin to seek help if you and your partner have been actively trying to conceive (ie. having regular intercourse, especially around the middle of the cycle when ovulation occurs) for over one year if the female partner is under 35 years of age, or for six months if the female partner is over 35 years.
If you or your partner have any medical conditions which may affect your fertility or have an impact on any resulting pregnancy, it is best to see your GP or specialist prior to trying to conceive.