I’m so selfish

My best friend is pregnant. It’s so frustrating because she already has two kids, one who just turned one. My fiancé and I have been trying for almost two years now and I can’t help but be so jealous. I’m happy but also sad. On top of that, she will be 8 months pregnant at my wedding which I feel like will take away from our big day. I know the way I’m feeling is selfish and bad, but it’s like no one understands.