It looks like your GP is considering secondary (central) hypo. This is where the hypo is caused by a broken signaling system rather than/or in addition to, a broken thyroid. When FT4 is below range and FT3 near the bottom your TSH should be much higher as your pituitary should be shouting loudly for more hormone but it isnt it is below range. T3 does tend to suppress TSH but it shouldnt when FT3 is as low as yours and FT4 below range.
Essentially you are under medicated but they do need to diagnose the pituitary dysfunction if its there as it would mean that TSH absolutely could not be used in dosing and will help prevent other GPs having knicker fits at very low TSH and slashing your dose in the future. It also means they will have to test the Frees each time not just TSH as is their wont.
If it turns out you do have central hypo it is worth searching Humanbean, I believe a lot of family members have central and would be a good source of advice.
Phoenix605 - Thank you for your very detailed and informative reply! Your description is somewhat similar to what my GP described to me about her concerns. I have read Humanbean's posts in the past but will pay closer attention now and particularly if I do have central.
The plan is to do pertinent blood work for pituitary issues and possibly follow with an MRI.
I get so impatient waiting for results of each change in medication. What I am currently scratching my head about is how to "guide" my GP as far as medication dosage change if pituitary blood work comes back negative. My guess is that she will only want to increase Synthroid - not Liothyronine because of the T4 and TSH being low. I was considering keeping Synthroid at 50 mcg. and slowly increasing my T3 by 2.5 mcg. (on my own) for the next week. And if all goes well bump it up again by 2.5 the following week.
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