If it's water retention you will have "pitting edema". Press your finger into the swollen part of your leg for 5 seconds. Does it leave a dent?
How far into sobriety are you? I've had little issues with water retention in my legs. Nothing major but my ankles can get puffy and I will have pitting edema.
It's funny you mention exercise. Yesterday I was walking for 4 hours non stop. My feet were so sore. I did a 12 mile hike/walk. I didn't have any swelling at all. I woke up this morning and there's a but of puffiness but no pitting edema. I have a feeling mine is either an injury, or this is just how it is for some of is in recovery.
I also have a round stomach. I am not sure if that's weight gain though because I'm 16 stone. I am working on losing 2 of those.
Keep us updated I am in the same boat although my swelling isn't that bad. It was very bad when I was drinking though.