If the pain increases on walking after a long rest, it can be due to plantarfascitis which occurs due to inflammation in the cushion like structure present in the heel. Consult a physiotherapist.
Next Steps
Go to a physiotherapist.. Ultrasonic therapy +wax therapy +some stretching exercises will be helpful for sure.
Health Tips
At home.. Rest +hot water fomentation +pain killer gel +no long walking +no cold exposure.