My Thyroid Was Removed In 2007 Due To 3 Tumors,

My thyroid was removed in 2007 due to 3 tumors, one cancerous. My Synthroid from the endocrinologist dosage was increased to 150 and I have been feeling fine except just the difficulty of losing weight. Two weeks
ago my GP ordered some blood tests including TSH. My medication was reduced to 137 mg. Doctor said I have too much hormones. I then researched TSH T3 T4 and found out that high TSH levels is only symptomatic of a non functioning thyroid. But why the reduced dosage