Vaginal delivery or C section?

Body: 

I am 42. This is my third pregnancy. I am 31 weeks now. With my son I had bad tearing and I was fecal incontinent for 8 weeks pp.The doctor told me is not from the delivery. I will be better. After my daughter was born, I found out I have cystocele and rectocele stage 2+ prolapse vaginal walls... I was devastated since in the same time they found I have 2 bulging disks in my lombar area that will not explain all my body left side pain for over 2 years now. I asked for a C section before my daughter was born. They told me I should not be worse. The damage was done at the first delivery. I did not have symptoms of POP before second pregnancy. Maybe I have a mild degree of prolapse that did not bother me. Both my children where big (almost 9 lbs ) and they have big head circumference.
I trust them but the labor was very hard comparing with the first one.I had bad diastasis recti and they could not find my cervix easy . It was out of alignment withe the vaginal canal and my daugher head was tucked under may tail bone. They were planing a C section after 13 hours of labour but they changed their mind in the last minute and put me to push with all my might! I felt so weak I barely pushed my daughter out... I tear bad again.
I cannot decide between C section and natural birth for number 3. I am sure I have some sort of uterine prolapse already since I could see my cervix low before. This is probably my last child. I just ask for some advice. I now that after delivery my POP will be bad again. I know I have no pelvic floor strengh since I cannot do Kegels for more than 2 seconds. I feel I cannot push the baby out so weak.

Your body is not a lemon! Your uterus is incredibly strong...it's held 3 babies in it. And big ones at that. When it comes time to deliver, your uterus is going to do most of the work, your baby will do a good bit of the work and the last tiny little bit of work will be your responsibility. And that's mostly in your head.
Eat lots of great foods, keep your iron up and get a birth team together. You do not have to tear this time at all! If it seems like your baby isn't in a good position when you are ready to birth think about changing the way you are positioned.
Have you thought about birthing on hands and knees?

anyway- all that to say, I think your body will be the best off not cutting through the abdominal wall. The damage has been done to your pelvic floor- and for that I'm so sorry. Mine is pretty busted up too. But in a few years you won't be able to tell the difference between 2 vaginal births or 3.
When you cut the abdominal wall you lose even more support for your pelvic floor because it's all connected. Also, since you have two little ones at home to take care of, your recovery is going to be so much faster with a vaginal birth.
we've had a great many discussions about c sections here and how exactly they do them and what it does to your body (anatomically) if you are interested. You can search the forums with the search function and find them all.
Good luck!