Plantar fasciitis is the most common musculoskeletal problem affecting the foot. The classic sign of plantar fasciitis is what is called ‘first step pain’, that is much more severe pain after rest, especially getting out of bed in the morning. The pain is almost always under the heel. So if you have pain under the heel and the first step pain, then you probably have plantar fasciitis. There are a number of other conditions that can cause similar symptoms, but probably around 90% of the time it is plantar fasciitis. The main risk factors for this are overweight, high activity levels and tight calf muscles.
The best way to manage plantar fasciitis over the long term is to reduce the load in the plantar fascia which is damaged. This is best done with foot orthotics and lots of stretching. The calf muscle stretching is absolutely crucial and need to be done several times a day of you are serious about getting better. Not all foot orthotics are created equal either and you need to make sure they have the design features that actually do reduce the load in the plantar fascia. A simple arch support design is not sufficient.
There are many other treatments for plantar fasciitis, but most of them are really directed at help the tissues heal which is not a bad thing, but they are less likely to help if the load is still present in the tissues. That really does need to be reduced. One of the best ways to to that is described in great deal by Running Research Junkie.