also get them to check your sodium level. A deficit or even if it is on the low end of the scale can cause edema, as the body is compensating with potassium.
Edema like this is often a symptom of a severe underlying disorder or disease condition.
You say your tests show everything "normal", but something is obviously being missed.
Specifically, I think your docs should focus on liver, kidney and heart function.
Keep pushing your doc for more testing. Don't let this go.