Well, of course I'm no doctor or psychologist, but IMO I'd say you pretty much identified it point blank - you yourself used the word 'obsession' about it. My heart goes out to you Chelsea.
Listen to me now...sometimes we can get so tunnel-visioned about things we want that we forget about the blessings that have already placed in our lives. You're a mother of three, and I know they're wonderful kids, right? And you love them as much as any mother could love her kids, I'm sure. They're blessings from God, don't let your thankfulness for them fade away. A lack of thankfulness to God for the things (and people) He's already given us can be a major reason for us not being able to receive more.
Also think about this...I kinda think you're envying other women who are expecting - you've left churches and often can't even watch them on tv...you don't want to see them with the blessings that you want for yourself. Really, that's understandable, it's human...but "where envying and strife is, there is confusion and every evil work."
Where envying is, your love can't work...and if your love isn't working, your faith can't work either, because faith works by love. Chelsea, don't worry about what others have. God is well-able to give you everything you want...there are a number of childbirth scriptures in His Word. Meditate on these, and on God's intense love for you personally. Let that flush out any envy or bitterness...God's able to do all things, and so is she who believes in Him
Lester