The Dr.'s will tell you that you should seek a Dr. if you have tried without luck for 1 year. THe thing is...NO DR. can explain fertility 100% as far as why women with all the "right parts" are not able to get pg.....it's frustrating, but like bigblues mentioned, sometimes people with unexplained infertility get pg. I HATE the term, "don't stress and it will happen". It is not because you are stressing out that you can not get pg....it's probably nothing you are or aren't doing...it just hasn't happened. I have had people tell me, "don't stress, lie with your feet up on the wall for 30 minutes after sex, put a pillow under your butt to elevate after sex, chart your temperature and cervical mucus, try clomid, blah blah blah".....we finally adopted and then still heard people tell us how now we would get pg. Nope! But I can say my girlfriend was going in for iVF and the month before she mysteriously got pg! So you can never tell. I do wish you the best of luck and want you to know that you're allowed to be frustrated with the process! You are not alone!
Best wishes for your growing family.