Your story is remarkably similar to mine that I wonder whether it is my birth story you're referring to regarding the nerve damage.
The only part where yours and my story differ is that I didn't have a reasonably painless time up until 9cm, instead I was having a reasonable, but nothing too arduous time and got stuck at 3cm. I was 40+14 when I went into hospital for a scan and they wouldn't let me leave (well, they sent me to antenatal to speak to a registrar who never turned up. I had been having contractions since 5am the day before and they suggested I stay due to some concerns they had with low levels of amniotic fluid so I just carried on having contraction after contraction in the antenatal waiting area. For many hours, because the maternity ward was full).
I knew nothing about the position of the baby as nobody checked, but I suspect he was posterior, as I had an anterior placenta and because of events that followed.
Eventually space became available on the delivery floor and I was moved there, introduced to my midwife. I was in not too much discomfort really. The only thing that really hurt was going for a wee. Something about when my bladder was at empty brought on an almighty pain that saw me writhing in pain. I thought these were contractions but I now know different.
Found to be 3cm still, after 50 hours of labour (20 so far in the hospital by this point) it was suggested they break my waters. I was exhausted and wanting to see progress, so agreed. Nobody checked for how the baby was positioned. Big mistake!
So midwife broke my waters and said: "I'll be back in four hours to see how you're getting on."
What followed was an almighty, searing pain that I cannot put into words. Like yours, the pain was constant or I'd get a few seconds of it easing, but then it be at absolute peak of pain lasting for, well I remember one went on for ten minutes. I went doolally, actually losing my sense of where I was in the room with the pain. I remember thinking that I had no idea I was even capable of feeling this much pain and why had I not passed out yet. And still I thought this was what labour was meant to feel like.
After three hours of this (I'm a stoic) I started to seriously lose the plot and remembered that losing the plot is a sign of transition. So I got DH to get the midwife in, convinced I must be at 10cm. Midwife checked me and I was.... 3cm still.
I could not believe it. How could all of that have been for nothing. And I had transition to come??!!! So then she suggested syntocinon. I agreed under condition I have an epidural first (I knew I could not take pain any worse than what I'd just been through. I still couldn't believe that that was supposed to have been the manageable pre-labour).
Well, the epidural failed (it had only partial effect) but it did take away the truly searing pain and left me with regular pain around the abdomen, like cramps. So I had gas and air for those.
I stopped using the boost button on the epidural and just let it wear off as it wasn't doing anything but by this time I was getting along fine with just the gas and air. It is at this point, I believe, that the nerve damage I sustained, was complete hence not feeling anything except abdominal contraction pains, which were hard but not mind-warping.
Anyway, synto drip got me to 10cm but baby wasnt descended so forceps got him out, the 10.5 lber that he was. Injuries to his face (not from the forceps, those marks were visible but different) showed signs that he was stuck sideways in my pelvis. Breaking my waters had been a DISASTROUS plan, as he had got wedged, as a pp suggested.
I was left with mysterious total incontinence that no one could explain, and catheters fell out. I was kept in post natal for a week while they investigated. A bladder x ray involved having a fluid syringed into my bladder via a catheter to fill it to capacity to check for leaks (or a fistula - their biggest fear). The radiographer asked, conversationally, how it felt and I said "pleasantly cool". He was shocked as I was supposed to answer "like I'm desperate for a wee". I could not even feel a sense of fullness, never mind hold even a drop of wee. He said he'd make a note of that, as it wasn't normal.
When pregnant with my second child my midwife kindly scheduled in a chat with the consultant obstetrician to go over what happened and make a plan for next time. It was he who explained that in all likelihood the baby's head was crushing nerves that run around the pelvis, in an effort to find a way through. Crushed nerves have only one way to signal they're being crushed: pain. And lots of it. He shook his head and asked why I had not asked for an epidural I was in so much pain. (Well the midwife had fucked off for a start, and I really though that that was what labour felt like).
Because it was such a long labour (contractions started at 40+13 and I had my baby at 40+16) the nerves conked out (and they took months to heal). The consultant assured me that normal labour would not feel like this. The pain would not be as bad. And if it was to see the signs again, I was to go for a caesarean. This was put into my maternity notes.
Well, ds2 was an easy-peasy labour in a birthing pool with just a bit of gas and air that I barely needed, if I'm honest (but was nice to have). I remember only one contraction that made me think "ooh what a corker that one was" and the next one had me pushing out a baby in big, satisfying heaves. None of the contractions I had with ds2 came even close to what I experienced with ds1. And I had none of the nerve damage the second time around, either.
The pain you felt was NOT normal. Believe me, I've had what you had and I've had a regular labour and the two are poles apart. I know I had nerve damage because it went on for so long (70 hours) that I suffered nerve shock and it took months for the nerves (for both control and sensation) to heal. Maybe your nerves were crushed too but just not for such a prolonged period that it got so badly damaged but enough to have sent you through the roof with pain.
If you decide to have more children, you may be surprised how easy you find it. I couldn't get over it. As I held my newly-born baby in the pool I said to the midwife "but, but that was so EASY!" because I remembered what my first had been like.