On average, most women will get pregnant with 6 months of unprotected sex.
But there are alot of things you can both do to help things along. Have you read any of the books out there about fertility and trying to get pregnant?
For instance, you should be taking your temperature every single morning when you get up (if you do not use a fertiity monitor) to chart your body temperature. When you ovulate and are fertile your temperature goes up.
Another for instance, a man should not use a hot tub if he is hoping to get his partner pregnant. The heat of the hot tub can effect sperm production for up to 4 months.
There are dozens of things you can do that might help. See a fertility doctor now if you like, but I would wait untiil it is six months of trying and you have read a book and made some changes in your life that make it more likely that you get pregnant.
Susan