Achilles tendonitis is often associated with pain is behind the heel where the tendon inserts into the bone. The tendon or bone may be inflamed. These symptoms often occur in runners or from wearing shoes that rub or cut into the back of the heel. Pain behind the heel may build slowly over time, causing the skin to thicken and swell. A bump may develop on the back of the heel that feels tender. Some patients also develop a bone spur with the problem.