Katkins,
Im just like you. I had bad pains too, and my cervix feel like its not tightly closed either like it once did before. I have a posterior baby too. I also felt the same back pain the other day as I did with the labor of my last posterior baby. I think you just have to not worry unless you loose your plug, have regular contractions or your waters break. I told my midwive yesterday this, and she didnt seem worried. If you really seem worried just ring the hospital.

Its hard not to worry when you are so close to reaching 9 months. Yes it seems your body is getting ready for the big day.

Good luck with your Vbac.