Perhaps it is a food allergy? That can cause inflammation/water retention. I am allergic to dairy (but not homemade plain yogurt, which I can't have now), so if any dairy sneaks into food/packets I don't pay attention to, I swell.
My sister is allergic to whey protein...so I have wondered about myself. I have reacted to certain packets with swelling and itching (the leek soup was the last I recall) so I avoid those now.
Maybe that is it because you are doing everything else correctly?
I totally understand the frustration!
P.S. Congrats on your loss so far; WoW!!!