So heartbroken/jealous of my SIL

My husband is currently away for military training, yet again! Back in February we decided that once he got home we'd start trying for a baby. We've been married for 2 years-been together for 5. So there's been a lot of talk around us having a baby, but we recently got military orders to transfer overseas. My MIL constantly tells me that I can't have a baby while we are overseas bc the baby won't know her, she won't be apart of his/her life, etc etc. On Sunday, my SIL announced to me that she was pregnant and they had been trying since February. Now, a lot of our relationship-I feel has been a competition. I was automatically heart broken bc I was like "seriously, she's been trying to get pregnant since I announced that we were going to start trying."  I feel like she beat me to my life long dream and is rubbing it in my face. I am so upset with my MIL bc I don't understand how she can tell me that she doesn't want me to have a baby yet, but her daughter is HERE having a baby. I've cried for days, now.  How do I get past this? I really want to be happy for my SIL but I'm so jealous that it makes me sick. I am beating myself up bc I want my own family so bad, and feel like now I really can't start trying. How do I love past this? How do I become happy for her?