You need your FREE t3 and FREE t4 levels checked ASAP. My daughter, (born w/out a gland-9years old) was on Synthroid most of her life, and had a low free t3 level. Remember that t4 is a storage hormone that must convert to the active t3 within the body for proper function at the cellular level! There are people who have issues with converting enough of the t4 to t3. For some reason,many doctors just assume that it just "magically" does so perfectly, but never, ever check! We as patients must be advocates for ourselves (& our kids in my case), and insist that COMPLETE labs are checked! If the doctor does not agree, then go to a doctor who will! My daughter no longer take t4 only medication. She is on Nature-throid (dessicated porcine) and doing very well. It has plenty of t3, so her body is not forced to struggle with converting any longer. Her good health is slowly returning (had heart palps, constipation,weight gain, fatigue etc...on t4 only) She no longer has these symptoms now that she has a more balanced level of thyroid hormones available for her body to use.
Sometimes Synthroid dosen't work until doctors treat the FT3 levels and adjust by adding Cytomel. Sometimes, you will need to switch to a natural thyroid med like Armour or Nature Thyroid, or becasue of the shortage of natural thryoid meds right now, some are using compounding pharmacies. Google compounding pharmacy in your area. They make the thyroid mixture for you there.
The downside is that many endos don't like to prescribe natural stuff, so if you go to Armour's website, they list doctors by zip code who will prescribe it.
:) Tamra