My father has a dvt in his right calf and has factor 5. recently his left calf is causing him pain and is becoming more swollen and tender. ?

Clot again/infection: He may have a blood clot if he's on blood thinners already for the other blood clot, then investigation with imaging would not change the management...he should follow up with a hematologist... Might benefit from a IVC filter to catch any clots from going to the lungs. If here's redness, swelling,infection/cellulitis is possible and he needs to see a doc to get abx

Dvt: This is certainly suspicious for another dvt which will be investigated by a leg ultrasound. His coagulopathy is best treated and followed by a hematologist and a vascular surgeon collaborating. Searching for an occult malignancy which may cause recurrent dvt may be indicated also at their discretion.