Yes Synthroid is a t4 only med. It is synthetic and a lot of people don't do well on it. You need Armour, which is a natural thryoid med, containing T4, T3 and T2 and T1 and calcitonin.
If you continue to take Synthroid you need to take lots of minerals with it, as it can cause bone loss. I bet the doc never told you that.
Armour does not do that.
Stopthethyroidmadness.com is a great site with lots of info, also 'Thyroid' Mary shoman's yahoo forum has lots of knowledgeable people that can help you.