Thanks Clem. I'm going to pursue medical options until I find out for certain what it is. I had considered tendonitis.
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BTW, my father had the same issue. Pain behind second toe, etc. He also had hammer toe(s) and last autumn had surgery that included shaving the second metatarsal in the toe to straighten it, inserting pins, etc.
I will do EVERYthing possible to avoid doing that. He recovered and is doing well but that surgery disrupts nerves, creates numbness and can create inflexibility in the toes/feet. It's a greater alternative than crippling pain IMO but I don't want any cutting on my feet.