What Causes Knots In The Arc Of The Feet?

I'm 38, 160lbs male and for about 3 years now been having problems with my feet, it started out with one developing a small knot in the arch, and over time has developed several and growing in size to be near a half dollar, they are also now in both feet, starting at the arch and now there expanding new ones to the sides of my feet and at the tops, the pain is excrutiating and I can hardly walk because of this.