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.
Answer assisted by David Miller, Medical Student