I am by no way a pro at this, but I am a woman. I just recently read this article, I am 27 weeks preg with my 3rd and his 1st. I want my bf to understand as much as possible to what a pregnancy does to a woman, physically, emotionally, and mentally.
http://www.webmd.com/parenting/baby/features/your-sex-life-after-baby you can read the whole article if you want. But this is very true for most women.
"Although it varies from person to person, most sexual issues women experience after pregnancy get better within the first year, according to the Mayo Clinic.
That first year with baby is physically intensive. During this time, both partners need to accept they might not be having as much sex as they did before.
It's also realistic to think that you may not ever go back to the way it was pre-baby."
It stated "most" and "within the first year" but some need longer, especially if she is breastfeeding.
I hope things get better I understand you are frustrated. But continue trying to understand, not all women are the same as you have found out sexually. So just because your ex may have bounced back after children, or never complained, or denied you when you want to be intimate, doesnt mean the current will be the same way.
Have you tried romancing her? Are you the same after the baby? Do you do all the things tht attracted her to you now as before the baby? You mentioned this is her first, so she prolly doesnt know how to seperate mommy from lover ... yet, but give her time and she will. Go out on a date night, let her know that she still turns you on and you love being intimate with her.
Wishing you all the luck!