26 lbs in 6 weeks does sound like water retention. Now here is my understanding of the bodies fluid system
1. The blood delivers the fluid and nutrition to the tissues.
2. The tissues then excrete the excess nutrients, wastes, and fluids around itself... this is called interstitial fluid.
3. This interstitial fluid collects at the lymph nodes... and becomes lypmhatic fluid.
4. This lymphatic fluid gets filtered as it travels through the lymphatic system, and eventually reaches the venous system via the lymph ducts.
5. Some of the fluid in the lymphatic system gets recycled because it can be reused by the system. However... the waste/excesses are transported via the blood to the kidneys and liver. And as the kidneys/liver filter the blood the wastes get removed and are excreted.
So if your retaining fluids... and its all in your legs. My thoughts would be that you would be having problems between steps 2 and 4. I would think that your lymphatic system isnt function correctly. If its all siting in your legs, chances are its not getting pumped back up to the lymph ducts where the blood picks it up. So just as Charlie says there is such a thing as a weak liver, I am sure there is also a possibility of a weak lymphatic system. And I dont know if there are any excercises that actually work ou the lymphatic system. I know that rebounding and drybrushing stimulate it, but do they actually strengthen it... I cant say for sure, but I doubt it. I mean your lymph should naturally be able to pump against gravity... rebounding doesnt seem like it would do anything except maybe make the lymph fluid easier to flow. Laying on your back with your knees at your chest... and gently rocking yourself back and forth would probably have the same effect.