Needing some advice

Delaney • Mommy to an angel 💙 Norah Grace 8/7/19💕🌈 Nylah Jean 2/27/23💕
So my fiancé and I have been TTC for about 7 months, yes I understand that isn't that long in comparison to others. I'm 20 years old and he's 24 and he has a two year old son.
My soon to be sister in law (who I can safely call my best friend) has a two year old who is three weeks younger than my stepson. She got a boyfriend and they've been together about 6 weeks. The other night she brought home pregnancy tests. She went in the bathroom down the hall and took a test. Moments later I hear her scream.
She's pregnant. 5 weeks and 2 days.
I threw up when I found out. How could this happen? 😭 My fiancé and I have been trying and she just accidentally gets pregnant. My heart is broken, and I almost can't stand to be around her.. All she ever talks about is the baby. She could be having twins since she's next in line. I'm just so jealous and resentful and depressed. I cried my eyes out for hours... I just need someone to talk to about it and I don't know what else to do 😔😔😔😔😔 I'm so discouraged.. I'm afraid I'll never get pregnant...