Why could one of my feet be swollen when i have no injury to the foot?

Is their pain?: I am not sure of your age but if you are young as I am presuming from your icon then you may have a stress fracture which could happen from a vitamin d deficiency as opposed to you recalling some history of trauma. This is one of may possibilities.

Veins : There could be a problem with the return of blood up the leg in the venous system.