Thanks for your input, I will call her office.
I don't get the impression your dr is 'intentionally' keeping secrets or withholding information. Obviously, she doesn't want to alarm you without knowing what's going on first. However, I agree she probably could have informed you why she is ordering those tests, especially the nuclear scan. I never had to get that for my thyroid but do get the impression it's beyond routine. But that's not automatically saying something awful is going on either.
Maybe you can call her office. Let her, or even her nurse, know you are wondering (as you obviously are), have been seeking out information and would feel better knowing beforehand why you are needing that test.
I would ask for a copy of the ultrasound report and then post it here. We can help you decipher what it says. Why was the thyroid u/s ordered in the first place?
And although its true, that most thyroid issues are nothing to worry about, you should probably at least know why she is ordering more tests.