lump on botton of foot

After beginning to play basketball again regularly, I have developed very painful, hard lumps on the bottom of each foot.
One has almost disappeared but the other one, located an inch below my second toe, is extremely painful to walk on, particularly in the morning and seems to get bigger. (I can see what looks like a grayish core just beneath the surface of my skin).
I find myself walking with curled toes so as not to put any pressure on that part of my foot at all and this has resulted in a painful stiff ankle and calf.
What is this and how can I get some relief?