Salt and water are really critical to success, as is magnesium. I don't think you've gained fat, but you may be retaining water if your kidneys can't process the bromine being pushed out. Minimum would be 1/4 tsp unprocessed salt in 1 quart of filtered water, three of these each day. You might do better with 4-5 quarts of salted water after your kidneys start processing better. Slowly your ability to lose the excess water will grow, though you'll feel uncomfortable for 3-4 days from the increased drinking water.
Sufficient magnesium will keep your bowels moving, which may also release more bromine from your system. I cannot stress enough how much relief I've felt from magnesium.
If you're not using the companion supplements in sufficient quantity while using iodine, you won't process bromine as well as you can. This could keep you stuck, not something we or you wish to see.