this is gonna make me sound like a horrible jealous bitch

This is gonna be a long one and I apologize bc it's gonna make me sound like a terrible person but I need to get it off my chest.... 
My husband and I have friends who are a couple that recently announced their pregnancy (she's 4 weeks). Everyone around me is getting pregnant and I'm horribly jealous but I am having a really hard time being happy for this specific couple. Here's the part where I sound like a terrible person... I've been telling myself through everyone's pregnancy announcements and every bfn I get "it's ok as long as _____ doesn't get pregnant before me" ... It probably happened for her first bc of my bad karma from thinking that. Anyway here's why....
He has a child from a previous relationship that he has full custody of. He was an ok dad who spent more time smoking weed than playing with his kid. They lived with his parents in a nice house and the kid had a good life living with his dad and grandparents. That is until he moved out to move in with this girl and he left his son at home with his parents. This was about 5 years ago now and the kid is like 14 now. 
Then there's his fiancé who has three kids of her own. She has custody of none of them. They are in custody of the state and have been for as long as I've known her (5 years). 
They got engaged about a year ago and I was genuinely happy for them. They started trying for a baby 4 months ago and she would text me that she thinks she's pregnant bc they had sex one time about two weeks into their cycle. So I didn't even think the trying was really that serious since they were barely bding. Meanwhile I've been getting busy like crazy since about the same time but I have very irregular periods from pcos so who knows if I even ovulate. 
They announced their pregnancy the other day and I'm having such a hard time being happy for them. Why is she so fertile and I'm not? Why don't you try taking care of the kids you already have? 
Again I know I sound like a terrible person but I had to get this off my chest. 
I feel horrible. I went off birth control three years ago and haven't had a normal period since. Me and hubby just started ttc a few months ago but I just know it won't be easy for us. 
I feel like I deserve a baby more than her and this is why I feel like a terrible person. Who thinks like that? Jealousy does horrible things to a woman...