What could cause sudden tsh spike ( after total thyroidectomy 18 mo) and t4 ok? tsh been 0.05-1.2 for 18 months then 6.5 and 9.5 (same day testing)?

Hypothyroidism: High TSH is indicative of underactive thyroid most likely due to switch of the brand ( from brand name to a generic) or poor absorption of thyroid hormone.' Suggest to adhere to the same brand ( no substation on the script), Take the thyroid hormone on empty stomach 30 min. before breakfast and AM meds and at least 4 hours before calcium, iron, vitamins, stool softner & antiacids