Crvena55
Have only recently joined this forum so I hope you see this post!
Hypothyroidism can have a number of causes, often either the gland is not producing enough hormone despite adequate stimulus from the Hypothalamus (another gland that controls the function of many other glands) or there is not enough stimulation from above.
What has probably happened in your case is that with the abnormal gland producing lots of Thyroxine, the normal production of the stimulating hormones (TRH and TSH) have been suppressed (called negative feedback). Now the abnormal gland has been removed, it will take a while for the TRH and TSH levels to come up, after which time the remaining thyroid tissue will hopefully produce enough hormone to mean that you do not need to take thyroid replacement any more. You may find that your dose just gets smaller. If you are getting any of the symptoms that people have described for hypERthyroidism (essentially everything working too quickly, especially heart, breathing and bowels!) then your dose may need reducing. See your doctor again
Hope that helps
Bob