I used to have a lot of water retention when I was anorexic. eating desorders can cause this,and IMO also emotional issues play a role. When I was extremely thin, I even developed hard coarse cellulite bumps on my back thigh/knees, it all disappeared when I was recovering . Reasons are many, I do believe that lack of protein/fat can do that.
I was told - but I did never try - that Bach Flowers remedies Crab Apple and Hornbeam are very effective against edema.
Remember that yr 1st concern should not be the way you look on the OUTSIDE but yr general health, both physical/emotional.