It is always good to have a balanced, healthy diet. Not eating consistently well can contribute to weight gain at any time. Cutting back on sodium ( very hard) may diminish water weight.
Also, there are things not to consume within about 3-4 hours of taking the replacement hormone. They are generally listed in the prescribing info but include things like soy milk.
Doc can rx a diuretic if you need one, but you have to watch your electrolyte balance when on one I believe