I'm constantly plagued with edema as well. Mostly in ankles, belly and upper arms. Just Cranberry mixed with water really helps but it's temporary fix. I stop drinking it for a few days and I'm back to square one. Also, it never totally gets rid of the fluid buildup. I drink PLENTY of h20 and still have the problem.
Edema *can* be due to chronic INFLAMMATION which is my case. The only thing that majorly helped was when I was on Naproxen and perscription muscle relaxers which obviously is not healthy long term so I'm no longer on it. The Naproxen reduced inflammation and the muscle relaxers helped me to void more completely. No doctor has an explanation or has given two hoots about my problem.
Hives are also an auto-immune response as is inflammation.
There is one way to test this theory for your selves. Take something with Tumeric - such as Planetary liver formula or liver cleanse by Solgar or just Tumeric by itself. It's a very good anti-inflammatory.
One other thing I found worked for me was a medicine for systemic candidasis.
But again, this is only a temporary thing since it's bad for your body. I'm still searching for a permanant fix - hoping the 'liver flush' will fix things.
Hope this helps you!