Your dr will have to do several tests on your urine to check out your kreatin levels and other levels of toxins in your urine or sometimes they can do blood tests to check on how well your kidneys work. I worked at a Dialysis unit for 4 years until I reinjured my back. But have your dr. Do some urine tests and blood work to make sure that everything is working properly, also they can do an a test that you take a couple of jugs home so that you can pee in there and they will check the amount of urine that you pass and to see if your kidneys are doing there job. I wander if you had your pancreas and liver checked also that is also a sign of Diabetes also which my husband has. So please do not put off these tests because fluid retention is not good especially if you have other issues also.
If you are concerned, I would call your doctor and ask him to test your urine and possibly do a kidney function test. That will tell a lot. If you are eating a lot of salt, this too could cause the edema or swelling throughout your body. Try laying off salty foods and cutting your salt intake. Good Luck. Feel Better.