The nuclear scan did not show any evidence of a stress fracture. That's good news, in a way, but bad news because I still don't have a diagnosis. My doctor initially had said "we will just wait and see." Wrong answer. I have been waiting and seeing for years now and this thing is getting better.
The doctor did say that I have a hypermobile big toe joint, and it could be that my second and third toes are getting recruited to take too much of the impact from walking and running. I also have bunions, which are not helping things either. Since my insurance has approved orthotics, I am seeing the doctor next week to get fitted for them. Hopefully that will keep my toes in place and I'll feel better.
The doctor removed all restrictions, so theoretically I could run. However, since I haven't done anything to fix the problem with my foot, there doesn't seem to be any reason to think it would be a good idea to try, at least until I have the orthotics.