Funny you should post this as I was thinking of asking the same thing. I got pg with DS # 1 the first time. I was 29. He's now 3.5 and we've been trying for # 2 and it's not as easy this time around.
I got PG last fall and lost it after 8 weeks. It took about 2 months.
We've now tried a few months recently and no success. I really thought I was PG last month but it didn't "stick" as they say. My Dr. told me to try for at least 6 mos before he'll do another check-up. I worry about secondary infertility as i've had a few friends who've had trouble having #2. I used an OPK last time and timed it out right, but there is still only about a 25% chance.
Mind you, this has only been a few months....I give those women who've tried for years sooooooo much credit. It's frustrating, disappointing and everything else. Best of luck to you.