What can cause Achilles tendon pain?

Tendinitis. If the tendon is inflammed, it results in Achilles tendinitis. The pain is usually resolved with physical therapy and anti-inflammatory medications.
Achilles' tendon . You may have injured your tendon which can cause by a tendinitis or a partial tear. You should be evaluated if the pain persists.
Overuse . Achilles tendonitis usually results from a chronic injury that occurs primarily from overuse. A lack of flexibility in the calf muscles may contribute to the development of achilles tendonitis. This causes the muscle to shorten resulting in more tension in the tendon. Other factors may include recent changes in footwear, changes in exercise training schedules, and hill running.