Sarah I can't provide a diagnosis but I have a similar problem, and I've come to the conclusion that it is some sort of inflammation in at least one of the tendons in the foot.
It does come and go, and I am pain free in some footwear (factory work boots) but other footwear (office brogues) make it worse. Taping has helped. Ankle stregthening exercises have helped.
I think we expect soft tissue injuries to heal in a few days or weeks, but in fact they can take months, even years. I think you should do all the things that help, and as few as possible of the things that don't, and hopefully it will improve
because it is a motorway...even with all those runners it's a very fast course. My clubmate pb'ed today from middle of the pack. It's easy to dismiss big races these days, but I remember when G
NR had lads who'd been out all night and decided to do it for a laugh, it's influenced millions of people to get out and run, in an area that sorely needed it at the time.
Looking back at your original thread, I am surprised that you were still racing in March. If you had those symptoms in January, and continued for another 8 weeks, you have done a lot of further damage
I considered the surgery, and after talking to the doctor I rejected the idea. He was of the opinion that if I could not walk or function day to day it may help, but it was not a long term solution and was in fact what he called "end-game stuff".
I am seeing a groin rehab specialist but it is really quite simple, special exercises for specific abdominal muscles, gentle uphill running, and 100% focus on the alignment and orientation of the pelvis.
Three months rest sounds conservative from my experience, but I know a guy from RW who has overcome the condition and is regularly running trail marathons on the south downs and turning in sub 21 parkruns.