I have a great posterior cervix story!
My midwife checked me at 38 weeks, 5 days, and I was 2cm, 80% effaced, baby at zero station, cervix soft and stretchy--but she had to reach so far inside me, I couldn't believe it. She said my cervix was completely tucked behind her head. I was so disappointed, but then my doula said to think of it like a bow pulled back, because she had seen many mothers snap into labor, no problem, after just such a position. I took great comfort in her words.
The next day, I had red show, but no contractions. That night, I woke up, not to a contraction, but to a feeling like THWAP, of a sudden shift. I started having erratic, painless contractions, but I called my midwife to check me at 3AM. She arrived at 3:30, and announced the baby was at +1, cervix anterior and paper thin...and I was 7 centimeters!! I had not felt even the slightest discomfort--we were laughing and joking quietly the whole time. My husband couldn't believe it.
I went on to have a completely painless labor, and gently pushed her out in two pushes into her Daddy's hands a couple relaxed hours later, as the sun rose. I'm still on a high from that gorgeous birth. I wish I could do it every day.
Try taking calcium LACTATE...it's just a calcium supplement, but it is associated with painless births. And be really passionate with your husband

. These things can't hurt, and may help a lot! I swear by them.