What Is The Treatment For The Edema In Feet, Ankles And Lower Legs?

I have had pitting edema (3-4) in my feet, ankles and lower legs for about six or seven weeks, accompanied by high blood pressure (last measure was 138/100, was 143/95 a couple of weeks ago). I am taking Lasix, 20 mg a day. I need to push my doc a bit to get tested to find out why I have edema (blood values are all normal), but my question is related to cortisone. I am scheduled to have injections in my knees for arthritis next week - is this going to be a problem? Is the cortisone contra-indicated given my current symptoms? I am a 46 year old overweight female.