Many, many years ago I complained to the "surgeon" on a Princess cruise ship that my feet were swelling up. In those days the ship's doctor on Englisn ship was called "the Surgeon" He recommended that during the night I keep my feet elevated by placing the life vest under the mattress portion where my feet rested. I swear it works with me.
Another suggestion is to ask for a low salt or salt free diet.
You might take ask you doctor if you can get relief usingretics such as dyazide or eqal.
Since I am not a doctor cannot give you medical advic; only infom you what has helped me while at sea aboard a cruise ship.
Often water retention that causes swollen feet is due to the food served containing too much sodium.