If hyperthyroid then hypothyroid then normal thyroid lasts, what tests needed to see why sleepiness cont. If no addiction or emotional problems?
Waxing - waning. Thyroid disease can often take a waxing and waning course, with thyroid function fluctuating between hyper and hypo, becoming normal for brief periods between. Eventually the thyroid "burns out" and stops functioning, leading to persistent hypothyroidism. Go back to your doc and see if this might be happening in your case. If nothing else, the chat should start you in the right direction.
Other things. Persistent sleepiness can be thyroid, low vitamin d & b levels, low iron/anemia, poor sleep due to apnea, restless legs, andropause/menopause, not enough exercise, too much caffeine. Talk to your doctor, other things are to try zeo(electromagnetic band that measures ur sleep quality& provides at home online sleep coach), avoid caffeine after 12, exercise, try otc calm's forte or melatonin to sleep.