Dear Cat,
The gold standard is what you have done, introduction leading to symptoms, eliminated by eliminating the offender. The synthroid may be affecting the situation by making you more sensitive, but the core seems to be what you have found. If you have any question, a confirmatory blood test could be done, but it is not as specific as elimination.
I hope this is helpful.
Christopher Maloney, Naturopathic Doctor
Augusta, Maine www.maloneymedical.com.
Informational only, I cannot treat or diagnose via the web.