Not happy for others anymore

I have always been a happy person. I am kind and genuinely care about other people. The longer I am TTC the less happy and more bitter I become. A young girl at the office recently announced her pregnancy and admitted that she didn't want a child right now. I smiled and excused myself to the bathroom and cried. My future sister in law is pregnant and I'm so envious. The longer i am trying the worse I get. I don't want to feel this way. Do any of you ladies have any tips for me? How to stay posi and happy for my friends And family.