Around where I am I often run in the lanes, but there are clearly two different sorts of drivers round these parts. Closer to the town, Colchester they tend to be impatient and prone to being knobs. On the Halstead marathon course in general they are excellent and give loads of room etc.
I have had the annoying close clipper experience in one particluar route that lead to only one place, so I ran to the village found the car noted the number and reported him. He buzzed me three time over the next few weeks and everytime I reported it.
After 4 reports from any member of the public regarding a "crime" the Police have to come and see you.
The youngman in question got a visit and I got loads of room from that day forward.
Upper back pain is almost certainly a result of a problem lower down.
The human body, can absorb an astonishing amount of damage skeletally before it can manifest as an injury.
You need to find a good sports physio. They will need to check you from your feet up. If there is an issue in the foot, it can lead to knee trouble, hip, trouble and here where the body really shows offf. The hip can twist and move a lot to ensure you stay upright and pointing forward. After the hip your spine will turn and twist until there is no movemnet left which often results in UPPER BACK pain!
You may also get away with visiting a good sports masseur.
The only real explaination for upper back pain is either a musular injury or an interconnectiveness of all things as laid out above.
If your current therapists are not helping you, it may be worth contacting any local running shops or clubs for recommendations. I'm in East Anglia and if you are anywhere near Colchester I can recommend an excellent physio who just got me back on my feet afetr 6 months of calve injury.