I agree with the previous poster regarding flaxseeds. They do promote regular BM's, and are a great source of Omega 6 oils.
I also have a sauna, and I haven't experienced anything as you describe. The sauna will help you eliminate the mercury with the benefit of bypassing the internal organs to do so. Also weight loss is another benefit of the sauna, so I don't see that as your weight problem.
Suggestions: Water fasting, or colonics to clear any bowel blockage.