Recently I spent 3 weeks in the hospital with pneumonia. While there, I was given blood thinners to avoid blot clots. A few days before I left the hospital, my feet and lower legs started swelling, particularly the right one. By the time I was ready to be released from the hospital, the swelling had gone down substantially. After a few days at home, the swelling began again and I was sent back to the emergency room to have a doppler ultrasound. The ultrasound showed no evidence of blood clots. Now a few weeks later, my right calf has become extremely painful. I can hardly walk on it and it is very painful to touch. There is no swelling. Although I have already had the one negative ultrasound done, is it still possible that I may have a blood clot?