Welcome to the forum, Bletherer.
I haven't heard of thyroid regrowth after thyroidectomy. Another member's thyroid has regrown afer RAI ablatement but it isn't working.
Thyroidectomised patients don't always do well on Levothyroxine only as their FT3 is often low even on high doses of Levothyroxine and T3 is the active hormone we need to feel well. Your FT4 looks reasonable but that doesn't mean you are converting to T3 well. If you can't persuade your GP or endo to test FT3 it would be worth ordering a private FT3 test from Blue Horizon or Genova via thyroiduk.org.uk/tuk/testin...
Ask your GP to test ferritin, vitamin D, B12 and folate as hypothyroid patients are often deficient/low and these deficiencies can cause musculoskeletal pain, fatigue and low mood similar to hypothyroid symptoms. Post your results with the lab ref ranges (the figures in brackets after your results) in a new question and members will advise whether supplementation is required.