Swollen left foot for 6+ years, suddenly getting worse. Now swollen up to knee. Tight skin. Red. Not warm. Blood test, xray & pulse all normal. Ideas?

Need US of veins. Should see doc to have a Ultrasound of veins as a blood clog is the prime concern. If no clot, then severe lymph or venous insufficiency or infection.
Foot swells now leg. I would worry about the circulation in the leg. Perhaps a vein is not working well to drain that leg or perhaps something is blocking the natural flow of lymphatic fluid. Certainly it does not sound like a kidney or heart problem since you only have one leg involved. I would also worry about it being red which implies infection or inflammation. You may need further testing.
Evaluation ASAP. Even without pain this should be evaluated ASAP. It is always a good idea when something supposedly stable suddenly changes.