Calf pain and swelling for 3 weeks (1cm to 3cm bigger) known blood clotting problem but d-dimer test ok, still possible dvt or something else?

Calf Swelling: Previous deep vein thrombosis puts you at high risk for recurrence. New leg swelling and pain should prompt an ultrasound. Although it is true that a negative d-dimer is a good test to rule out venous thromboembolic disease in low risk patients, no test is perfect. If you are a high risk patient, particularly is swelling is progressing up your leg an ultrasound is recommended.