It’s sod’s law, isn’t it – you worry for years about getting a woman pregnant by mistake, then when you actually want to, it refuses to happen.
You do need patience when trying to conceive. Sometimes it happens right away, but sometimes it takes ages for no apparent reason – and if you want medical help you are required to try unaided for a set length of time (although thankfully they don’t ask you to present proof in the form of date-stamped photographs or anything). On the upside you get to have a lot of sex, although some couples find conception sex lacks spontaneity and becomes a bit… unsexy.
If there is a medical problem, be supportive of each other – it can be a real blow to your self-esteem to find yourself deficient in the reproductive department. If it's to do with her biology, remember, it's going to be a huge blow to her self-confidence too, so be supportive.
This can also be a good reason to not tell people you’re trying, because then you don’t have to explain your problems to anybody later, or raise your parents’ hopes of grandchildren only to dash them if your conception problems prove insurmountable. However, if you do choose the keep-quiet approach and then manage to get pregnant, be prepared to be asked whether it was planned. A lot.