After Mowing My Lawn In October, I Started To Get

After mowing my lawn in October, I started to get pain along the back of my lower left leg. I had to sleep with my leg extended out of the bed. Slow the pain subsided and then I started to get sharp stabbing pain in and around the bottom of my left foot. Still sleeping in the same position, the pain seem to abate after I got up and walked for a while. At times I can walk about a half a mile and the pain would return in the back of my leg and stop after I sat down for a few minutes. What can I do? The pain now returns even with my leg extended while I sleep.