Right leg is swollen and hurts. Hurt it years ago running and it keeps swelling and then goes down and swells again. What could cause this?

Swelling of leg. If the leg swelling is recurrent and subsides overnight but reoccurs later in the day, I would be suspicious of chronic vein damage which might be an aftermath of the old leg injury which may have caused phlebitis. If the leg swelling is not in the leg or ankle, but in the knee, it suggests cartilage damage. If it's not a knee problem,consult a vascular surgeon for evaluation and treatment.