I was on Synthroid for about three years and continued to experience classic symptoms. Following my own research I requested a natural thyroid "Armour" and have had great success. My general Dr. did not want to prescribe it because pharmaceutical companies push Synthroid. My Endocrinologist didn't hesitate to prescribe 'Armour'. I feel so much better! My general Dr. is more open minded now that he has seen my results.
Synthroid, as you probably know, has a long history of problems in manufacturing ranging from sub-potency, stability, variation in dose in the same pill and reliability. Do a google search. There are other products available, such as the natural product from Armor. In my opinion the risk from animal products is minimal, although there has been discussion of prion contamination.
There are cases of allergies to the dye --- to avoid this, use the dye-free 50mcg (0.05mg) tablets -- in your case take 2/day and one day a week take 3. Usually it's another allergy, but it's worth eliminating the possibility of dye allergy.