Feeling down

Seeing post about people being pregnant is driving me crazy. Not that in not happy for them its just that im ready for it to be my turn. When does that day come? I've been patient. I've been waiting so when do it get to feel that joy? My sister is due may 6th. She is having a little girl and is getting married. I've been waiting 3 years for all of this to come for me and instead she gets it. Wow I sound a little selfish. Yes I am very happy for my sister and I love my niece with everything I have. But its kind of not fair