I Have Noticed That When I Have Been Running (ok,

I have noticed that when I have been running (ok, probably more like jogging) or walking for a while, that I tend to develop this lump on my leg. It is only on one leg, and is not every time I run, but is becoming more common and it feels a little bigger. It is not there all the time, only after I have been running/walking for maybe 10 minutes, (walking takes a little longer) and it goes away after a little while of resting without any ice or anything.

It is located on my left leg, 3 inches above my ankle but then an inch over (toward the front of the leg) and is about the size of a half dollar-ish, but it sticks out maybe half an inch or more. It is not very painful, but that area will feel very, very tight and I will also get twinges of nerve pain (like electric shocks) when it is swollen and while it is calming down. I do have some issues with nerve pain, so that in itself isn't new, but the fact that it also swelling is concerning. (it is not red or anything, but if you feel it, it is quite firm)