Your doctor should also have ordered Free
T3, along with the Free
T4 and TSH... Free
T3 is the thyroid hormone that individual cells in the body actually use, while FT4 is more or less a "storage hormone" and must be converted to Free T3 prior to use... It's possible that your body isn't doing the conversion adequately.
Your FT4 is at 58% of its range, which is higher than the recommended 50% of range... so your thyroid seems to be producing adequately.