My legs, ankles and feet swell day or night. I don't drink, smoke or do drugs. Why does this happen? I have had edema (swelling) in my legs for the last two years.  No doctor has been able to specifically determine why.  I have been told it is 'allopathic'. Whether I sit, stand, or lie down, the swelling is always the same or becomes worse.  My skin is so tight it is uncomfortable and sometimes painful.  I have a prescription diaretic, nova-hydrazine, but do not like taking them.Travelling by plane is now impossible due to the extreme swelling which occurs as a result.  Car rides are becoming difficult, too.  My feet go numb within minutes. I am otherwise in good health, and exercise every day, walking at a speed of 4 miles per hour for an hour a day  on my treadmill. I have excellent heart-lung ratio.  I have been tested for diabetes (my dad has it) but it is negative.  I am only 41 years old and am worried that this condition will seriously debilitate my life. I do have Sacroilitis due to Ankylosing Spondilitits, but am not sure how this is linked. Any suggestions?

Summarized question: What are possible causes of chronic edema in the legs, ankles, and feet?