Why?

Why is it that the people that want to have a child so bad cant seem to get pregnant but people who don't try and don'teven want children seem to get pregnant. This is something that I will never understand. In the past 2 years I have had 2 cousins under the age of 18 get pregnant and a best friend that didn't want to be pregnant. DF and I have been ttc to quite sometime now and every time we hear the news that someone else we know is pregnant it is heartbreaking. I try to put on a happy face around my family and friends and act that I am so happy that they are getting exactly what I have been wanting for so long. At the end of the day I ask myself "What are we doing wrong?" " Why not us?" We have a great relationship, a great support system, and the want and desire to be parents. Why cant we have what we have been wanting for so long? I pray that god will grant me the courage to continue on our ttc journey.