You could have something called plantar fascitis. It can be caused by a number of different reasons. In plantar fascitis the big tendon stretching along the bottom of your foot becomes inflamed. At its worst it can be incredibly painful. I had it at one time and it was cured by getting orthotics.
If it is plantar fascitis stretching your calf muscles may help or orthotics but you really need to go to a doctor to find out what's going on and, if you need orthotics, to get good ones.
Good luck! As bad as it is if it is plantar fascitis it can be solved. Check out the URL's below.
http://www.healthcentral.com/chronic-pain/guide-154667-75.html
http://www.podiatrytoday.com/article/1559
http://www.virginiaheelpaincenters.com/