I am a 28 year old female. For the past 2 weeks I have had intermittent moments of quick pain in my left upper leg. They began my my knee and have since moved up to my upper thigh. The pain comes and goes, and it has occurred both when I am walking and when I am inactive. I am very active (I exercise daily) and walk around all day as a teacher. I take birth control. I am worried that I may have a blood clot, but am unsure. Any ideas?