P.W.
Yes, it could be a stress fracture. that happened to me, but the pain became so bad I couldn't even walk.... so if that is what is going on it is probably mild and wearing a boot for a short while would allow it to heal.
If it is tendonitis I can tell you my husband had it and it was really defeating him. Then I began my own wellness business and put him on a vitamin program. He felt better in many ways, but the one that surprised us was that his tendonitis was helped. He used to have several bouts of it a year that lasted several days each. It was ruining his exercise program as he had to stop exercising as advised by the doctor with each bout, but since on the vitamins maybe two short bouts in 2 years. It's amazing what nutrition can do! If you decide you would like more info on what he takes just let me know.
In the meantime see a podiatrist.