Not to cause worry where it is highly likely that none is warranted but you may want to mention it to your doctor.
You never know when a piece of information might be useful, so thanks for adding that.
Funny, the day after I wrote that, I awoke with what felt like a stitch in the middle of my back. And... it turned out to be a pulled muscle from sleeping in a funny position.
I'm telling you, there is the voodoo in the air!
Hey Mike, by any chance was the pain in your back anywhere near your broken rib(s)?
Several years ago I had a serious bike accident with injuries similar to yours, including some broken ribs in my back. After I was healed enough to start running again I experienced pains much like what you described. It seemed odd because they only came on after I'd been running for a while, typically around an hour, plus or minus. It was worse and happened more quickly when orienteering and having to run bent over a lot to duck under stuff.
I chalked it up to a combination of fatigue and muscle weakness and endeavored to stretch and strengthen the area. It took somewhere between 1 and 2 years to be fully over it. Long enough that I wondered if it might be a permanent condition. I hope this doesn't become a recurring issue for you, but it sounds so familiar I thought I'd mention it.
Fossil, broken ribs are all on one side, and the muscle pull is on the other side, so it's hard to suspect they could be related. That said, it wouldn't surprise me if a full recovery doesn't take a while. I'm still something short of my full, normal lung capacity.