Heel pain is common. There are a few possible causes of it, however there is one cause that is most likely. Regardless, I believe you need to see your primary care doctor
for a proper diagnosis. In addition, this likely requires treatment and he or she can help provide it.
Heel pain that you are describing is classic for Plantar Fasciitis. The plantar fascia is a thickened ligament type tissue that spans the bottom of the foot. This area of the foot can become inflamed if overused. Some people are predisposed to this, often based on the "arch" of the foot. Improper or no shoes can sometimes worsen this. When this gets inflamed, people experience pain on the bottom of the foot towards the back. This is often worse with movement and it is classic that the first step of the day is the worst. There are treatment options which include foot braces
and most often inserts into your shoes to support the arch of the foot. Inflammation can also be reduced with pain pills.
Other causes include a fracture
of the bone or skin infections. Muscle or tendon problems are also possible. Talk to your primary care doctor. This can be treated. Good luck!