I can not give you a specific cause as I have not examined you. When I have a patient present with these symptoms, I will x-ray to rule out a fracture, infection or tumor. I will check for an ingrown nail, I will do a neurological check. I will carefully go over the history and look for things like diabetes, sciatic nerve problems, other neurological problems such as neuropathy.
As you may guess, this is not so simple to diagnose. I suggest you see a podiatrist.