I read about this (worrying about problems with soy due to my own thyroid issues), and apparently the problem is with unfermented soy - things like tofu and soymilk. Fermented soy, like tempeh, is supposed to not cause this. I don't know: I tried tempeh a little while ago and around the same time I had a thyroid flare-up....but whether the soy caused it or not I don't know.

I've been exploring vegan diets and have indeed encountered Freelee and her boyfriend (I think) Duranrider. They're....strange. I mostly found Freelee after the internet blew up when she said non vegans don't deserve to live. I'm not a big fan of ultra-restrictive diets. Similarly, I believe she exercises a lot - it's the only way she can reasonably maintain her weight while consuming thousands of calories a day in fruit. Also, I'm not where she gets that veganism is a "live well" type of thing. Veganism is just about avoiding animal products for whatever reason. Exercising and sleeping well have nothing to do with it.

If you're going to watch veganism videos I highly recommend Unnatural Vegan. She's freaking awesome: her videos are well-thought out, a little blunt but also sympathetic, and she holds moderate views and values that don't make vegans look crazy.

About supplementing: certain vitamins are not available in plant sources. B12 and D3 are among them - they need to be supplemented. Technically, you can get B12 through something called nutritional yeast. It's used in a lot of vegan cheese recipes. D3 can be supplemented...if you can find vegan sources. Which are generally expensive (the other day I learned that vitamin D3 supplementation is a wool byproduct. Strange but true).

As to managing mental health through food - I think it can be done, it just won't work for everyone. I find my moods will do whatever they please regardless of what I eat, except for certain instances like binging.