Mystery of the Fat Calf

Usually I blog about races or new shoes and gu's, but I have an issue that has at least a minor relevance to running that I can't find a solution for. It's the mystery of the Fat Calf. It is a swelling in my left calf that happens at various times, I usually only notice it when I'm going running. The whole calf increases in size and is very, very tight when you push on it. It feels tight too, like someone is squeezing the top of your calf with their hand. It's not there all the time and I don't know that it's caused by running.
Originally I thought it may have something to do with running on unlevel roads since it's only one leg, but even this winter when I have been forced to only run on the treadmill I have the problem. My next best guesses are sitting with my legs crossed at work or the high heels I wear at work. Not sure exactly how either of them actually cause the issue, but it's the best I can come up with.
Since it's not swollen all the time I think I can rule out a blood clot, but I just don't know what the next step is. Like most runners I don't want to run to the doctor each time I have a minor pain or ache - since we have them more than the average Joe. And, like a lot of other runners, I have yet to find that doctor that meets my running needs. It doesn't seem to matter what issue I go in for I seem get the same answers - "you should probably cut back on running" or "you might want to think about not doing that race". She's great, she's just not a runner and doesn't know what it means to me. Not running is the solution for everything in their minds - they don't look at the benefits only the toll it takes on a body. Anyway, because of this I haven't been to the doctor, but I have looked online. One promising thing - I did find some posts of others with the issue, just no solutions or causes. Someday I will find the answer, until then I will run, fat calf and all.