Dangerously low Thyroid problem...S.O.S.

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Hello
I've been battling a dangerously low thyroid for almost 6 years now. I am on Synthroid, and am watching what I eat, and working out. With the help of my sister showing me this site, I have been able to keep on track more.
I was wondering if there are any foods that I MUST avoid or any kind of work out that might help me out even more.
I appreciate you all!!

Thanks!