I think this is pretty normal. It happens to my husband (who came home after a run with only one sock, because he had to use the other sock in the bushes...) and apparently this happens to a whole bunch of people, especially when they start to become active.
Check out these links on the subject:
From Runners World:
http://www.runnersworld.com/communit...n%3A8031008354
From Time-to-run:
http://www.time-to-run.com/doctor/runnerstrots.htm
From the Mayo Clinic:
http://www.mayoclinic.com/health/run...arrhea/AN00376
From The Western Journal of Medicine:
http://www.pubmedcentral.nih.gov/art...?artid=1021858
Quite possibly the most embarrassing story invoved Paula Rutledge, the British Marathoner, who just couldn't hold it in anymore and had to do a very public BM along the side of the route at mile 22 of the London Marathon in 2005. In front of thousands of spectators, and a million viewers LIVE on TV...
So take heart! Just keep at it. You ROCK!
Kira