The Graves antibodies can continue attacking TSH receptors after thyroidectomy. TSH may take years to recover and sometimes never does.
I think your endo reduced dose from 100mcg to 75mcg because your TSH 0.07 is below range. Your FT4 20 was comfortably within range so you weren't overmedicated on 100mcg. Reducing dose has seen your TSH fall lower so your endo will hopefully be guided by your FT4 and reinstate 100mcg.
Oh dear. Another TSH worshipper! He reduced your dose because your TSH was low - not quite suppressed - even though the FT4 was reasonable. You were not over-medicated just going by those results. But as j.bee says, you need to see your FT3, that's the important one. So, now, your FT4 is much too low, which means your FT3 will also be low. Never agree to a reduction in dose based solely on the TSH. And it might be a good idea to change your doctor!
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