There are diuretics that do not affect potassium as much as others and you can take potassium supplements. I have to take 60mg daily and still have fairly low potassium but it stays in the low normal range.
Has your doctor tested your urine for protein? Does your urine froth? That is an indication of protein being filtered out by your kidneys and will cause edema. Do you have any other circulatory problelms?
My first guess would be that you have something going on with your kidneys. Other than that I don't know what your problem could be but would pursue it with your doctor or see another doctor and try to get to the bottom of your edema.
I had both edema and inflammation. My edema was caused by my kidneys (proteinuria) and the inflammation was in the muscle tissue and was caused by either/or lupus or polymyositis (an inflammatory muscle disease). In the early months it was quite severe and it definitely was not like the pitting edema that proteinuria causes.
MCTD (lupus, scleroderma, polymyositis). Diagnosed 2005. Kidney, liver, GI tract, dysphagia, raynauds, Barretts esophagus, quadriplegic in 2005. Recovered and now active in skiing, tai, chi, hiking, golf. Meds: prednisone 2.5mg, imuran 50mg, amlodipine, benazapril, omeprazole, potassium, folic acid, vitamins, maxide and various supplements and vitamins.
Remain optimistic and you can overcome the odds.