From your original poste which is indeed barren from a medical point of view,it is a matter of "lucky dip"...pays your money and takes your chance.
With the above provisos, I would suggest that it is either a condition called plantar fascists or an acute flare up of osteoarthritis of the ankle.
My advice is to take Ibuprofen 400mgms every 6 hours or more if necessary and monitor the situation for the next 7 days.