A baby is conceived when a male sperm cell fertilises a female egg cell. For this to occur, an intricate series of biological processes is required. Falling pregnant is an extremely delicate process, which is why a prompt conception can never be taken for granted. You should not be disscouraged if you have not fallen pregnant within a few months - a waiting period for one year is not uncommon.
In cases where couples have engaged in unprotected intercourse for a period of one year, without resulting in pregnancy, they may be experiencing problems with fertility. For more information see: Failure To Conceive.