How can I tell the difference between a blood clot and a cramp? I have what feels like a pulled muscle, not very painful, on the back of my leg a couple of inches below my knee on the muscle there. Nonsmoker, no hormones, no plane trips, not obese (5 2 /115), 41 year old female in good health with no history of blood clots, but I did just take a 12-hour car trip (I was not driving; I changed positions and got out a few times for walks). Thanks!