This is from APMA (American Podiatric Medical Association)
WHAT IS CAUSING MY HEEL PAIN?
The number one cause of this pain is condition called plantar fascitis. It is characterized by pain on the bottom of the heel when you take your first step in the morning, but it can also last all day long, often progressing the longer the condition remains untreated. Other common causes of heel pain include tendinitis, stress fractures, neuritis, bursitis, tarsal tunnel syndrome, arthritis and fat pad thinning.
Plantar fascitis can be caused by a number of factors, including weight gain, worn-out shoes, walking barefoot, increasing exercise and walking on hard surfaces without proper support.