Med Q: Lump in leg while jogging

Okay, so I’m jogging on the treadmill, and had been doing so for about 10 minutes, when my leg started getting a burning sensation down the side. So I look down, and a lump about the size of a marble has formed on the side of my leg. (Bout halfway down, area between muscle and bone)
It’s squishy and about 1cm in diameter and height.
After about 5 minutes I get off the treadmill and head to weights, and after about 15 minutes of not running, the lump is gone.
Is this common? Should I be worried?

Are you prone to spider and varicose veins? I’ve got a varicose vein in my leg that I only notice when I’m exercising. It’s right below my knee on the inside of my right leg and will swell to about the size you’re describing. It goes away when I’m not exercising (or standing on my feet for long periods of time, I no longer work retail so that helps) so I haven’t done anything about it. Anyway, that’s my best guess…

There’s probably something to be said for having a doctor check you out for this one.