How do you know the culprit is soy?
Those foods -- cabbages, etc. -- are not bad foods, but highly nutritious and will not cause you to have thyroid problems; if you have
a thyroid problem, you would be advised to limit them.
I would go to the doctor for a concrete diagnosis instead of wondering and worrying about what it could be. If there appears to be a thyroid problem, then worry about finding treatment. It may not be a thyroid issue at all.
I will link some things for you to read and a site page with various resources below.
I think there is valuable information HERE
you should read from a doctor who advocates a plant-based diet.
And Dr. Fuhrman has a few words
on soy and hypothyroidism you should read.
(If you want more information from Dr. Fuhrman, let me know and I'll do a search for you).
You can also ask local hospitals
if they offer alternative medicine.
You can look through THESE
links for alternative med info/practitioners; if some don't work, then do a search for them on Google or other search engine.
Personally, I would not hesitate to take advantage of Dr. Fuhrman's phone consultations
since I don't live in NY; however, if I did, he'd be my first choice of who to trust as my primary physician.