What is the exact location of pain?.. If its at the heel and back, it can be plantarfascitis, generally occurs after a long rest, specially in the morning when you come down the bed...if its at the right side of ankle after any twisting of ankle while walking or something, there can be any ligament injury... If its at the mid of sole, it can be die to flat foot.
Next Steps
Go to a physiotherapist.. Ultrasonic therapy +wax therapy +some exercises(stretching/strengthening) will help.
Health Tips
At home.. Rest+hot water fomentation +pain killer gel +no long walk+no cold exposure.