I agree with Nutmeg about getting your antibodies tested but not so much on the soy though I understand where she's coming from. I also think that if you are taking Synthroid, even the lowest dose, they should at least monitor your Thyroid levels (Free T3, Free T4, & TSH (most only monitor TSH)) 6 wks after prescribing the Synthroid then every 6 months after that. You don't want to go hyper on it. It's good that your dr is thinking outside the box & willing to try things other dr's probably won't but you really need to be monitored IMO. Even if you are sub-clinical hypo, those tests should show it, i.e. you would be at the upper end of normal, I would think.
About the soy... if you are sub-clinically hypo, soy is technically a no-no since it is a goitrogenic, meaning that it slows down an already impaired or slow thyroid. But to be honest, I (knowing this) could possibly see myself doing soy in the future since 1) you only do it for 5 days, 2) if you're on thyroid medication it should correct for the slowness the soy may cause, & 3) it works like Clomid which we know that I need Clomid or some other O-inducing drug to help me get pg.
You may consider dropping by the
Thyroid Disorders board... there is lots of info there & several ladies that can answer questions (myself & nutmeg included

). GL & don't stress too much... I'm sure your dr is taking good care of you.