They are now finding that it is from a gradual breakdown of the tendon it's self. Pain along the tendon, which can be confused with a lot of different injuries. Usually the pain comes from going up and down stairs and general pain when pressed. Also pain when the tendon is stretched. Rest until you can perform some type of low rep exercises with really light weight.
Ice really hits the spot.
As soon as you can start exercising safely, then do so. Also a appointment to a ortho to see if you need orthotics is a must. Some anti-inflammatories will help. Mostly anti-inflammatories only mask the pain. In this case they can help to shrink and take out the swelling.