You could try natural thyroid medications, like Armour, which is a pig thyroid preparation containing porcine T3 and T4. However, if you are responding immunologically to the Synthroid, eventually you could also do the same to the porcine T3 and T4.
I don't know how your physician determined that you were responding immunologically to the Synthroid, but this is certainly possible and could negate its effects by its removal.
You could also try Tirosint. It is T4 like Synthroid, but it is in gel form capsule. It supposedly does not have the added fillers of Synthroid and the generics.